I have a Helion Dominus 10TR 1/10 scale and my spur gear keeps stripping. I correctly mesh the pinion and spur gear together. I use the paper trick. Does anyone know why the gear keep stripping? My only guess is that the motor moves after jumps or crashes but the motor is still secure in the same spot. Again does anyone have any advice?

Does your car have a slipper clutch installed? If it has, it can allow the spur to slip in case of extreme loads, saving the motor, and transmission. If it has one, chances are it's been too tight, and barely allows slip. While this gives max acceleration of grippy surfaces, it will also mean the pinion/spur get every single added load transferred directly.

Is the bearing/bushing that supports the spur gear wobbling or loose at all?

They dont have a slipper clutch that fits the Dominus TR. The slipper clutch made is only for the SC version. I tried to put one on already. So the slipper clutch is out of the question. And there is nothing that is loose. Everything is tight.

If you can't put a slipper clutch on it, you'll have to land with the power off unless you enjoy replacing gears. Landing under power without a slipper will make short life of any gears without a slipper.