Lee, here's another thought while you have it out. Even if you get it working perfectly, the vacuum wipers will always be lacking. When the vacuum wipers on my '57 began acting up a few months ago doing the same thing as yours, I decided to check a couple junkyards looking for the factory optional electric wiper motor instead of trying to fix the vacuum unit. The electric version was available as a factory option for the Task Force Chevys and I think that it was standard for the Blue Chip GMC's. Maybe I got lucky, but I found two in the first yard I checked, one out of a GMC and one out of a Chevy. Both worked fine. Bought them for $10 apiece. I figured I'd buy both so that I could have a spare.
They connect to the dash and the wiper arm assembly using the exact same hardware, bolts, brackets and cable knob as the vacuum unit.
The factory units were two speed...slow and almost fast enough...and self-seating.
The cable knob that operates the switch is the same as the vacuum unit. As you turn the knob, the cable moves the slider switch on the motor. A partial turn activates the motor to slow and a more complete turn moves the switch to fast.
Wiring is easy. It is designed to have the + wire always hot and the switch works on the - side of the circuit. Bolting it to the dash handles the - side, just make sure that the metal is clean. The factory connection to the + side was to run a wire through a grommet in the firewall and connect it to the ignition switch side of the ballast resistor on the firewall. That simple! Wiring it that way allows it to operate only when the ignition switch is turned on. I ran mine through a fuse block, but the stock factory installation did not include a fuse block.
Sharing only as an alternative. I am much happier with the electric wipers and I was able to keep things factory. It's not much fun to work under the dash, so I thought I would mention this just in case you want to consider it as compared to fixing the vacuum unit.
Matt
