You can find Ofna, Jammin, and HotBodies diffs pretty cheap on Ebay. They are all basically the same and work with the RCM output shafts. I know for the Jammin and HotBodies you can use the hardened steel internals which last a lot longer than the cheap cast pot metal stock ones. I use the hardened steel ones in all my diffs for my Jammin and Nexx8.
http://www.hotbodiesonline.com/produ...hbc8101-1.html