"Final drive" to me means the rear axle, however I assume you are referring to something else, as front wheel drive would still work, but what? primary clutch secondary clutch, gearbox, what? Any of that is going to cost a lot. All of that is going to cost as much as the bike is worth. Find out what is wrong first, then get it fixed.

 

 

Dismantle it and see what the problem is the gear should be cheaper than the whole assembly and they are not bad to replace.

 

I priced out the parts and it actually made more sense to just get a brand new unit. $279 for the ring gear set, $160 for friction discs (they're worn to the indicator), and $90 for a bearing & seal kit. To me the $50 I'd save by rebuilding it wasn't worth it.

 

Yes, Yamaha are odd, in that a new rear axle seems to come out every couple of years, they never settle on any design. I note on new ones they seem to have gone back to external disc brakes. So your chances of a used diff are slim. Best to check what is wrong first though, the solid rear axle models used to wear out the axle splines in the crownwheel and I have known prop shaft splines to wear out too. So, if it was a similar fault on your machine, it might not be the gears you need.