Equa-Torque, Trans-X, and there's one more. You can't use a synthetic oil in a clutch pack diff. KAZZ runs their diff oil (non synthetic) at 80w-90. If you run a synthetic oil (for anything OTHER than a clutch-pack), you don't need the tube of friction modifier (but adding it won't hurt anything).
The first number of the oil designation is the weight when cold, and the second part is the weight when it heats up.
If the R33 diff isn't a clutch pack, there is a company out there that makes some fucking BOMB ASS diff or tranny fluid.
http://specialtyformulations.netfirm...alog/index.php
They're closed for a short Christmas move, but their fluids are created with Group IV & Group V basestocks. I don't think you can even buy a Group V oil in a retail store..