craziness

last week my 86 N/A started making a really loud clank from the rear end. reminded me of a CV joint going bad, although thats not the case. the car will drive, but i have to really take it easy. my question is this: is it common for the trannies to go bad? What exactly does break? my car has 135,000 miles and ive never had a problem with it since ownership (109,000). Another question i have is this: My car really runs rich and my mechanic has no idea why! (funny thing is, he really knows his stuff) He installed a new MAF and that helped a little. i notice that when i let off the gas, my oil pressure guage drops more than normal. Anyway im worried about the tranny and am wondering what a replacement would cost.

Sam guards red '86 944na

ram_one

My tranny imploded yesterday. No warning. 103K miles.