I posted this on SF but this is a motor specific section
MB Slot Krahs. FC-130 Wasn't running well. Slow and smelt of escaping electricity (smoke)
Took the endbell off (wiring still attached to the chassis)
Removed the arm/endbell as a unit
Removed arm.from endbell
Cleaned between comm segments with a toothpick
Cleaned up comm a bit with 1500 grit wet'n dry
Put arm back into endbell
Put endbell/arm back in motor
Put the motor back into the car and it ran backwards. Had to reverse the lead wires at the guide!