the motors need to be blown out of carbon dust every service
if the brushes wear to the point issues occur ie wide steering or pulling to one side then scrap the motors don't even bother trying to rebuid them we get at least a 50 percent recall on rebuilt wav motors
when installing new motors or new brushes, the brushes need to bed in without load
i wire up the new motors but do not bolt to the "gearbox"
then power up wav bridge foot switches, tape over presence sensors and tape throttle in full speed forward for 20-30 minutes and same reverse

having said that no other motor seems to need this much care
and we still get about a 5 percent recall doing it this way
the new motors we haven't had any problems......yet