I have seen many sedans stripping gears now Kyosho, Mugen, you name it the .12 engines have alot of power for a small package. And I think that the chassis's are flexing some and causing the pinions and spurs to move farther from each other resulting in larger gaps. Then when the car hits second well there is goes. The teeth that is. Just what I have heard and seen. Think about the this as on a 1/8 scale the actual thickness of a spur gear is almost double the thickness of the 1/10 and the engines are only under 1 hp less. only 1/3.