I can't find a part # for the pinion gear that is attached to the center driveshaft cup in the rear diff. I noticed that the rear end quit pulling and dissasembly revealed a cracked pinion. :ack
I was just looking around on ebay and there are some GPM diffs on there that are a different type of plastic thats supposed to be a lot better. They are blue. I cant get you a part # right now though, sorry.