Chosen Solution
The motor gets hot and stops in a few seconds. The commutator has burn marks and beads of metal(?) alongside it. I have measured the resistances between each adjacent segment on the commutator, they are all between 3.5 and 4 ohm each. The brushes seem to be OK. Does the insulation break down? I tried cleaning it up but it goes bad the same way when turned on for a few seconds.
@alanport yes you will need a new one. the wires are insulation coated. It gets hot and melts and shortens out. There are places that rewind those but the cost will most likely exceed the cost of a new motor
