has anybody bought a used ring and pinion and had good luck with them? Motive performance 3.73 on backorder for who knows how long, and everybody says don't use richmond gears, so now i'm thinking used GM gears on e-bay.

 

I would advise against. Strange also makes a good set of gears. They whine a little more than Motive/GM gears but they're still solid gears. You simply don't know what you're getting is used gears.

 

I would also recommend going with some Strange Gears. It is pretty hard to accuratley inspect gears over the web. You want to inspect for chips and wear pattern on the gears.

 

I agree, do not buy a 'pig in a poke'. New ring&pinion sets are not that expensive...
As for the Richmond, I have them, and they howl pretty bad. Some say once they're set up correctly they shouldn't whine, but a lot of people complain about them anyway.
Good luck