Ad says it needs a rear pinion gear. Any idea how big a job is that? What might that cost?

 

Crownwheel if it needs that, about $200, pinion $100, non genuine bearing kit about $50. Worst part of the job is fitting the needle roller bearing for the pinion, or rather, getting the old one out as it is held in by a snap ring, can take 4 hrs to get the old bearing out, weird thing is, there is no reason to fit a snap ring, as the bearing can't come out once the pinion is in place. I never put the snap ring on the new bearing, and never had problems afterwards.

 

That's my experience, too. I put aftermarket ring/pinion gears in a Honda TRX300FW rear end, and it was very tough getting the old bearings out. Used R/Es at the time were $500 on eBay.