I just tried right now. I removed the piston, spring and spring guide, closed the gearbox and was able to spin the bevel gear freely with my finger.
But what I also just tried was connecting the motor up without it connected to the gearbox with my battery attached and now the motor doesn't even spin at all when I pull on the trigger.
Anyways, I hope you can help me diagnose the problem soon and Merry Christmas!
