build a gmaxx and i need help

[suicideneil]

Depends what you mean by 'any kind'. if you use a MOD1.0 spur gear, you need a MOD1.0 pinion gear ( same deal with 32pitch spurs and pinions ). If you mean materials though, then hardend steel pinions are the best, or hard-anodised aluminium ones. Mike sells arguably the best hardend steel pinions around, then there are also the RRP ( robinson racing ) pinions, Novak's pinions & a few other brands- hardend steel is the best to prevent a steel spur from eating the pinion within a few runs; standard aluminium ones like you find on ebay wont last very long at all.

Your diffs wont break if you dont use grease, but they will probably wear down a bit quicker and be noisy- any kind of grease can be used, so long as its a bit sticky and preferably symphetic. That tamiya grease is easy to find on ebay, as are automotive greases used in 1:1 car gargages- check out your local hardware store or shop that sells stuff for 1:1 cars.