The bevel gear is plastic and the main diff gear, which is quite large, is aluminium. HPI should of released the car with a plastic diff gear or sold a metal Bevel gear as an upgrade part. They could of made it a proper Tamiya M-Chassis competitor if they had just spend a bit more time designing and testing it. Handling was pretty good I thought, did take some work though. If they had of done an upgrade gear, I would still be running it now!
The gearbox is sealed, you can run whatever grease/lubricant you would like. But I tried many, nothing worked.
Tamiya FF03 Pro ~ Tamiya M06 Pro ~ Tamiya M05L JCW Coupe