Think I figured it out (if anyone has similar trouble in future). The wiper shaft nuts were very loose, likely causing the mechanism to bind. Tightened the nuts, cleaned the blades, and applied RainX. Wipers work fine now on even a dry windshield. Probable didn't need to change the motor after all, but at least I won't have to rebuild the spare now.

6 VOLTS/POS. GRD. NW INDIANA

I would Rain X the windshield. In fact I Rain X all the windows in all my cars, love that stuff.

"The Master Cylinder"

Enjoying life at the beach in SOCAL

Try a coat of car wax on the windshield.

  

My vacuum wipers work great (rebuilt motor/fairly new vac. tubing) when I wrap rags around the blades, but on a wet windshield they hang up. The blade rubber is ancient, but looks pristine so have never felt the need to replace. Has anyone out there with vac. wipers ever seen a big improvement in function (less drag) with new blades? (I only change my electric grocery-getter wipers when they start to smear). I also wonder if the latest high-silicon rubber formula is available in a 50s configuration, and would that make a difference in friction?

6 VOLTS/POS. GRD. NW INDIANA