From the factory, the front differential is filled with SAE 30,000W
viscosity silicone oil. The rear differential is filled with grease, but can
also be tuned with silicone differential oil.
Only use silicone oil in the differentials. Traxxas offers SAE 10,000W,
30,000W, and 50,000W viscosity oil (see your parts list). The
differentials have to be removed from the vehicle and disassembled
to change/replace oil.