any tips on replacing AZB auto transmission in 92 100S?

I have bought a replacement automatic transmission (AZB) for my 92 100S. The
replacement was pulled from a collision wreck and was reportedly working fine
at 92K. Cost $300. Fluid is clean and not any traces of burning. How hard is it
to do the job? Any special tools needed besides a transmission jack? Any tips
REALLY appreciated. While under warranty this 92 100S had THREE tranny
replacements. Is there something that the dealer mechanics missed that is
causing repeated failures? I drive really easy, never tow, and have kept other
tranmsmissions working for many hundreds of Kmiles with no problems. I know I
may be wasting my time putting in a fourth tranny, but I really like the car
and the engine is in great shape. Thanks, Mark