Ok I have a small tip if you havent tried it yet.

I stipped out TONS of gears like what is happening here. My fix was to simply support the front and rear of the motor. The gears strip under race condition upon impact off jumps. The SLIGHTEST little flex of the motor causes the pinion to strip.

I have done 2 different fixes so far.

Front and rear of the motor. Use aluminum angle and drill it out to the exact size of the motor and bolt it down to the chassy. You will not get any flex of sudden movment. Since I did this I can run 1 set of gears for 10 or more races.

I also used a monster heat sink. I simply drilled a straight piece of aluminum to fit his mounting hole for rear support.

Try those you should get results.