Earlier I had posted my problems w/ my heater blower motor on my '70 142 in the post "142 heater blower motor troubs". It turns out the bushing in the motor has worn out. There's just enough slop in the bushing to allow the shaft to hang up on the brushes. You can hold the motor upside down, allowing gravity to help center it as it spins, and it will run fine. Hold it upright as it's mounted in the heater and it instantly leans and sticks once it's powered up. The slop wasn't very noticable the first two times I tore the heater apart, and it seemed to run fine whether it was rightside up or upside down, but the problem was quite pronounced this time.

I was thinking about having the motor rebuilt but I cracked one of the plastic brush holders when I was freeing the fan blades from the motor. I think I have a factory replacement lined up. The Siemens brand motor I had ordered earlier was not a match.