I've...
I've refurbished a 244, 234 and 264. Most Portastudios are very similar on the inside.
Replacing the capstan belt is not that difficult, but is a moderate teardown of the unit. For FF/RW problems there are the "tires" on the clutch assembly that's a bit more embedded in the mechanism, and would be a pretty significant teardown.
This is not rocket science, but it's a good amount of disassembly, including many small screws, cables & connectors. You'd need at least a basic-to-moderate techy skills to do these repairs yourself,... or if you started out a rank novice on this, you'd be a moderate techy when you're done!
There's nothing wrong with having a qualified tech refurbish this unit, but you'd save a ton of money by doing it yourself, provided you got in and out cleanly affecting a fix without breaking it or causing other problems.
NOTE: I just remembered, if you want a really good pictorial explanation of the refurbishment of a Portastudio, search for Dr ZEE's posts and on his personal website he has the refurbishment of a 244 pictorial,... also a 144 (I think). It does a good job of explaining the steps and showing the guts in pictures.
FOUND THEM:
TEAC 144
TASCAM 244