As most of us know, these old vacuum wiper motors are old, are wore, are not working very well and need work.  Some time ago I made a tool to fit the goofy heads of those little bolts that hold these things together, pulled one apart and took the paddle out, it has thin leather around the edge.  The problem is, these leathers are supposed to be loose, free to move and be pulled against the area it moves back and forth in, the vacuum pulling the leather to the body, sealing it as it moves and giving full vacuum power.  Here's what I did to loosen my leathers, I filled a container with Neat's Foot shoe oil, put the paddle in and let it soak for a couple of days, then took it out and VERY carefully lifted the edges of the leathers a little, being careful not to break or crack them, then soaked again, did the same again and soon they were free and back to what they were like in the '50's.  I coated the inside area with a light grease, then put it back together again.  Also, clean and oil the little spring and flipper valve, make sure it clicks and shifts back and forth when you move it thru' cycle, with luck your motor might make those wipers do quite well again, mine did.  Vacuum wipers are FAST when they're right, much faster than electric replacements.
warren