tranny problems

hey i got a question for the last month ive been having leaks in thru the rear main seal of the tranny . ive replace it several times. I finally narrowed it down that the tail shaft went bad. I have a aw4 transmision . can it be easy to be fix or should i buy a rebuilt tranny. i also have a 350 winser with tranny and drive shaft would it fit and would it be realistic to bolt it on my 91' xj and fit my rear end .

thanxs

is this truck four wheel drive. if it is two wheel drive, then the drive shaft seals against the rear of the tranny housing, similar to the back of a pre-95 4wd t-case but without the t-case. if the truck is fourwheel drive the seal between the tranny and t-case actually rides on the t-case input shaft which isn't hard to change, the output shaft on the tranny requires removing the torque converter, pump, all planetary assemblies and clutch packs. basically everything needs to come out to get to the output shaft in the back of the tranny