Its been a while since I had my 122's rear axle apart but i seem to recall a procedure to set up the mesh of the crown and pinion involved changing shims behind the backing plates or shims near the pinion bearings.

If you take it apart put he shims behind the backing plates back the same. Otherwise you might need to check the gear mesh with blueing and get the mesh correct. i think there is a felt seal you can change in front of the backing plate. I remember seeing a drum where a misplaced brake drum key caused the surface on the drum where the felt seal rides to become distorted.

I made a tool to pull the drums and some I had were really stuck on the tapered portion. i remember heating and cranking on my puller and beating on the puller to shock it, When it finally came, that drum flew away from the car.

i think if you at least loosely install the drum you can then install the key with it already on the taper, and then you wont get that key situated too far back and cause the issue with the drum cracking near where that felt ring rides.