After replacing the muffler, I could hear that the blower would only run at HI speed, so I bought a new resistor. When I pulled the old one, I saw why it had overheated - a squirrel nest in the squirrel cage. Part of the blower was chewed away, causing it to vibrate, and the motor itself didn't spin freely. Penetrating oil followed by engine oil in the blower motor's bearings seems to have fixed the motor, but I'll have to replace the squirrel cage, and wash out the evaporator core when I convert to R-134a.

Blower Motor Siemens PM249; Motorcraft MM527; Visteon 100066
Blower Motor Connector Motorcraft WPT041
Blower Wheel Motorcraft MM1071, Siemens BW9308 (smaller metal)
Blower Motor Resistor Motorcraft YH1698; Wells JA1176; Standard RU318 or w/pigtail; BWD RU1013; Dorman 973-011 (973-412 with pigtail)
Blower Resistor Connector Dorman 973-307; Standard Motor Products RU318; ACDelco 15-80675



It also required these repairs:

.

****UPDATE****
After several months, the motor is still working fine.

Owner caption November 2009 · Photo 34 of 434