Hello all. I know motor break-in is a smart thing to do in order to properly break in brushes, but keeping that motor clean is equally important. Any r/c shop sells motor spray. The carbon from the brushes has a nasty habit of fouling the end bell on any electric motor. This build up will cause excess heat and arcing on the commutator. Spray the motor until until only clean fluid runs out and re-oil the bushings periodically. The improvement is instantly noticeable. Most motor sprays are plastic safe. Hope this is of some help.
Regards, JZ