How often do you need to change the out put shaft on the 1995 mitsubishi 3000gt

Should not have to replace it all that often. If you are having issues with it wearing out and leaking I would consider inspecting the cv axle. How old is it? How much play is in the axle? Also are you buying quality seals from auto zone or another good auto parts store or are you getting the cheap ones on line. I bought some cheaper ones on line that were suppose to be as good as oem but they were not. Ended up having to replace all the cheap seals with quality ones.

Your car is 20 years old- that's not long lasting enough for you?!

im confused bearings aren't the same thing as seals,, so how you gonna put a bearing in where a seal goes,

If what I think you are asking for is a way to re-machine the crankshaft front and rear seals without pulling the crank out, in effect there is, it is called a silver seal and it is a press fit paper thin steel sleeve that is press fit over the sealing surface of the crank so that the seals have a new smooth surface to ride on. These engines over a hundred thousand miles all need this treatment because the seals wear groves into the crank and then the seals leak. So that's what to do if the front and rear seals leak---or if the cam shaft front seals leak.. Pull up their video when you google silver seal. You have to buy a $20ish tool for putting them on, too. They work.