"Do you know of any universal motors that have thermal protection?"

Good point Leon.

Larry, what have you been doing with your 621? I've got one that is
about 4 years old and never a problem. In fact I have 625, 12" SCMS,
palm sander, biscuit joiner, cordless trim saw, 14.4V drill (and two of
those at work), and an 18V drill. Never had a spot of problem with any
of them.