Your original question was quite difficult to answer without specifying what gearbox you were talking about. Am I to understand that it was the Wattage 370 gearbox, such as on the Crazy Max? The only place I know of that might sell parts for those is Hobby People.

BTW, Wattage 370, Speed 300, and GWS 300 are all the same motor. I think that's why you like them so much