G.I. Joe

There's a broader context that's informing that, beyond which vehicle is easier to sustain.
The Aus Army is pretty small. They aren't going to invade anyone or go anywhere without friends, unless they can do it purely with light infantry (eg East Timor, Solomons). In particular, in any large conventional fight that friend is going to be the US. And wherever the US goes, they build an astonishing logistics infrastructure, which means that parts and base support for M1s will be right there.
The Germans might be there too, but they will not provide the same shared logistic support.
Therefore, on Operations, the Abrams will have easier logistics than the Leo.

Ah, now we are talking about our competitive advantage.  Bottom up democracy is much more resilient and agile, but does trade efficiency.  In the warfare that a certain nation considers theirs, they have always been hobbled by their own addiction to centralized authority and structure.  If one is going to do systems-based non-linear warfare - less structure, more agency and meritocracy are the better qualities to leverage.  It is nuts but we need to re-wire approach, they would need to rewire their entire society - we can crush this competition but we need to wake up first.  

You've had answers of the required depth from people who've been there and done it and here's one from another 'been there done that guy' - short of putting on a green suit and trying it yourself what has been posted here is as good as its going to get to convey the message.  From the information and analogies in your posts, it is clear you are focused on each individual tank and its operation by the crew in complete isolation.
You seem to be in rather a hurry and the reasons you articulate for that are sound but, the weather and ground conditions are iffy for large scale mechanised operations so the time is better spent training rather than rushing that kit to the front line.  History is replete with examples of how rushing stuff to the front line causes problems, British tanks at the Somme in 1916 and Tigers and or Panthers at Kursk being two vaguely comparisons relevant to the situation now.  Time spent in training and rehearsal is well-spent and lots of people here have rightly criticised the Russian military for launching this operation in a half-bottomed manner and equally criticised the quality of the troops that have turned up as a result of the mobilisation.  It would be unwiser than an unwise thing for Ukraine to adopt exactly the same courses of action as its never time for amateur hour in warfare.

And of course there is training people up to a level of proficiency that they do it on zero sleep while someone is trying to kill them part.  And then training them to not kill each other by accident. And kill the other guys well in a disciplined manner.  A lot of this is pure muscle memory which does not immediately translate from one platform to the next.  Last thing you want is a crewman to react as if they are in a T72 while in a western tank.

All of this applies to fighter jets as well, except you have to be able to do it right the first time upside down while pulling seven Gs.

Ok, well just skimming the wavetops here…going from 3 crewmen to 4 is the first real hurdle. Totally different internal systems so maintenance and operation is going to be different.  Different capabilities which will drive how the crew will fight the vehicle (hell they will likely have to learn to live in it first).  No point in getting a new platform if they intend to fight it like their current fleets.  For example western tanks reverse much faster, which drives an entirely different tactical fire and movement procedures.  Different fire control systems and gun behaviour (range, penetration etc), western systems are more point and click but then there is the battlefield comms and info sharing suites.  Ammo handling, damage control and recovery are also different.  
And then you get into specialized drills like minefield breaching, water crossing and snorkelling, all different from Soviet equipment.  In some ways when it comes to crew training I expect that untrained crews are going to be easier to train because they do not have to unlearn the old systems first.
Also western tanks are designed to be fought in platoons of 4, not sure if the UA does the same or fight Soviet style in platoons of 3.  This opens up collective training with just the tanks, based on numbers we are talking up to Company as a minimum.  Training a company to march, shake out, deploy, fight, consolidate and sustain through all phases (offence, defence and withdrawal) is going to take some time as again these are fundamentally different systems.  I expect if UA crews treat them like the Soviet stuff these western tanks will be broken pretty quickly.  Western systems take a lot more TLC.  And then once you do all that, unless you want to relegate the armor to being on its own, you then have to move up to combined arms training and integrate infantry, artillery and engineers - rinse and repeat on the phases of warfare.   Most of these units are going to be in various types of equipment, likely some Soviet and western mixes which is going to get a little weird. You have to do all this without breaking your new tanks or getting people hurt.
And then there is the logistics train.  All the maintainers, recovery folks and specialists that the UA do not have and western nations are not going to put in country.  And then all that has to learn to keep up with the new combat teams, that should not be moving like the current UA armor (see: indirect fire) or what was the point?  So now specialized logistics trains are going to need to learn to keep up with stuff like break through.
Oh and before anyone brings it up, this is crash course speed.  Because the UA will be cutting corners and accepting risk, not too much or see Broken Tanks.  So 6 months is at break neck speed.  This is not moving to a slightly more modern vehicle.  This is a completely new weapon system that takes 4 people to operate it.  Its inherent capabilities and quirks drive how it is employed at basic levels. Upscaling those change how the units that employ these vehicles are organized and operate - in a contact sport where you do not get many second chances. 
 

In the larger picture, it's pretty fascinating to observe the "WTF is taking so long?" vibes.
This conflict is 11 months old. Ukraine lost 36% of the country and regained 18% back in that time. Something like 4 or 5 major land campaigns have been fought out. The air/drone/missile war has gone through multiple iterations. Casualties are something north of 300,000 and vast global political and strategic forces have been transformed. 
I blame social media (or the internet, or video games, or something) I guess.

I am going with @Lethaface on this one.  We are in the middle of winter and other than some dry humping by the RA there is not much going on.  The reflex is “oh my god, the conflict is frozen!”  So the follow on “send them the entire German military!” to keep things unfrozen makes sense…from a certain point of view.
I suspect - also from that video Steve posted - the weather has not cooperated and it is too muddy for any major UA operations.  It took the UA the entire summer to set up for the Fall Offensive, so if a major winter offensive is off the table it is not because the UA is unable to attack, it is because they do not want to.  Conditions are not right and it is more advantageous right now to let the RA break its hands at places like Bakhmut.
 

Capt...you know better. This time next week it will be "Where are the F$&#ING JETS??!!!?!?!??!"

Yes.

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

As a Marine Grunt, about the only thing I know about armor is to stay the hell out of it’s way, but the Abrams question might simply be due to fear of the technology getting into the “wrong hands.” When I was a USMC F4 Phantom II mechanic in Japan in 1971 (I had two jobs in the USMC, Air Wing and Infantry) it was very safe duty because the U.S. Navy prohibited our F4-Js from being used in VietNam because they were too new and too technologically advanced. Perhaps it’s the same thought for the M1A1s or what ever they have. And yes, I have no idea about the configurations of the ones they “gave” to Iraq or Afghanistan. I’m pretty sure that we even “de-tech” platforms that we sell to our staunchest Alliies.

Love the new yellow and blue colors.
Here's hoping we will see more Western made aircraft painted in these colors this year. 😁

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Yeh, for all we know the Pentagon may have simply looked at the bridge ratings across the country and said "Oh...lets not send them Abrams after all." I recall back in 1999 the US march into Kosovo turned into something of a farce as they struggled to get their heavy MBTs from point A to point B.

This is nice refreshment from previous beaver discussions.😉
Interesting that still most Chechen corps fights in southern sector. They seem to delegate only small detachments to Bakhmut offensive. I wouldn't read too much into it by itself, they have developed contacts with Southern MD, but worth to note nontheless. Moving them as rear troops  for mobiks in the future may be one of indicators where Muscovites plan to strike.

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Fun fact: ostriches don't actually bury their heads in the sand - while they guard their nests, they lie with their necks flat along the ground, which creates the illusion from a distance.
(Don't mind me - spot the birder / natural history buff).

Very well, add "actually threatens us" to the list.
Sadly, we allow a lot of small Mordors to exist and don't give a damn if their orcs plunder, pillage and rape in Rhûn or Harad. Not if those Saurons help us make our rings of power.

Here's a thread where O'Brien dissects what he said exactly - and it is quite a bit more optimistic:
 

This is not about settling the bills nor revenge, but purely pragmatic international policing- we can't allow this Mordor to grow. Unless you want your kids/grandkids to be conscripted into new, enlarged Bundeswehr and spend significant parts of their life on constant watch over some river or forest in Baltics, Poland or Finland against North Korea 2.0 armed with nukes and several mlns soldiers. Like many Western and Eastern Germans did for two generations against each other  by the way.
 
Some clips from Bakhmut, better to turn off music:
 

Fair enough. But if you really mean that kind of moral approach, the West is in for a really unpleasant wake-up call. We all have blood on our hands. We all do business with dictators and we all look the other way as long as their victims suffer and die in a far away country and preferably have a skin color different from ours.
Ukrainians are just lucky (if that can be said about their situation at all) that their country is next door from Europe, that their enemy is a country many have old bills to settle with and that they look like many of us.