What wears out ?
sliding parts like bearings brushes and slip rings.
Insulation on the wires can get abraded away if they're allowed to vibrate, and excessive temperature can make it brittle and crumbly.
Insulating varnish can break down chemically from excessive heat. That's the "Burnt" smell a motor emits shortly before failure, often accompanied by smoke..
Allowing dirt and grime to accumulate will block flow of cooling air and it might get into your moving parts.
I recently fixed an expensive electric saw by simply cleaning grime out of the brush holders - it had jammed the brushes in place and they lost contact with the armature.
Fixed another one that had a fractured brush holder, likely from thermal cycling because it had got covered up with sawdust.
Just soldered a piece of flexible wire across the fracture . Now the rigid brass part is free to shrink & swell a little bit with temperature..
Keep it "Taut Clean and Cool" is one of the fundamentals of electrical maintenance.
Designers allow for thermal expansion that occurs with changing load. Probably this particular holder fell victim to tolerance stackup.
old jim
