The item you're referring to is the Slapmaster Tools thrust bearing assembly. Not inexpensive, but very worthwhile over the long haul. Brian has been running the same bearings in his 1/12 car for at least a couple years now and maybe more. No more bearing replacement every few races, less maintenance, and a smoother diff to boot. The kit runs $30--I am installing them in both my cars I'm building up for this season. Contact Brian on
Slapmaster Tools
Scottrik