Older Kenmore canister suddenly quit, then restarted for 2 or 3 seconds, stopped for a few seconds...restarted...stopped...etc. The run spurts seemed to grow shorter and the stopped intervals seem to grow longer.
But I didn't leave it on to see what might happen as there was a lot of sparking at the commutator during the running "spurts". I replaced the 19 year-old brushes, but nothing changed.
It's a single stage blower, current Kenmore # is 4368931.
I should add that the armature spins freely on new bearings installed 4 months ago. At that time, a spacer washer was overlooked and left out. Another one was installed while shooting this problem, to raise commutator a bit for better brush contact.