If its not broken don't fix it....
As long as you grease the input shaft into the engine coupler, which had a grease fitting on it, and you have no water leaking into the blige from the drive bellows you should be fine.
Your car goes 100,000 miles, as the u-joints are self seal lubricated.
Hopefully, your mechanic has open the set screw at the bottom of the out-drive to check for water in the drive oil.
After four years, I would have the manifolds checked for leaks, as water could get into the engine....