Optics are mounted in the mantle so large calibre strikes on the mantle can damage them. This is only a noticed issue if your mantlet armour is thick enough vs the guns it faces that the worse thing that happens is the sight breaks up due to non penetrating hits.
Hamptmann Bollert OC, I abt, Pz reg 2, report 9-19 October 1943 : The telescopes of the T.Z.F 12 gun sights break apart as a result of hits on the gun mantlet. The expenditure of protective lens for the T.F.Z 12 is very high. ( 1995 Jentz pg 138).
There's a reason why gunsights tend to be roof mounted nowadays. Note one of the features of the proposed series production Panther schmalturm was a periscope gun sight, so they knew there was a design flaw in mounting sights in the gun mantlet.
The long 7,5cm was also recorded to have been put out of action by AT rifle penetrators bulging the interior of the barrel rendering it inoperable.
Bastables got a reaction from GhostRider3/3 in Problems with spotting
