Hey Sperry,
I just installed the small and large mounts because the holes in the chassis are not round, they are slots and you move the motor to get correct gear mesh.
The problem is: when you have a crash / do jumps or the screws just simply come loose, what happens is the lay shaft gear and the diff gear come out of mesh and the lay shaft gear gets ruined.
By memory a new lay shaft gear costs about the same as the small alloy mount so you don't want to chew these up very often.
My MT is about 4 weeks old and I would highly recommed replacing the Large Mount at a very minimum.... also get yourself a pinion & spur gear cover as small rocks really trash the spur gear big time.