My old craftsman shop vac started to smell "hot", like the motor was burning
out. I removed the top cap over the motor, and verified that the brushes were
fine. On further inspection, I discovered that there were two wires that had
broken loose from their commutator connection. I carefully heated the wire end
with my soldering iron, then scraped the insulation with a knife, and scraped
the connection point on the commutator, and then soldered them back in place. It
now seems to be working fine. FWIW.