Change automatic gearbox from 91 with one from 89

This is quite urgent question.
I I Intend to change automatic gearbox from 91 with one from 89.
My gear box leak ATF, I ask in ZF service and they ask much money to fix this problem. So, I find out good second hand automatic gear box from Audi V8 3.6l 1989 in perfect shape.
Is there some difference between my automatic 4 speed gear box from 1991. V8 3.6l and this one (from 1989, 4 speed automatic gear box) I intend to put in?!