Today I am fixing another Fostex R8 where the plastic capstan wheel was slipping, and the spooling motor wheels did the same. This is a common problem with these decks.
Fortunately, John from https://www.tascamninja.com/ makes aluminium replacements. Replaced the belt also. Now, the deck plays and spools perfectly.
But unfortunately, a problem remains: the arm on which the right tension roller is mounted, has got a fair amount of play, causing the roller to guide the tape in a skewed position. It is not a show stopper, but it is certainly not ideal for the tape path.

My website with a lot of other information: https://www.reeltoreel.nl/