The symptoms: your wipers move slow, and in very cold weather may not move at all.

The repair: remove the motor and add modern grease, and a drop or two of oil.

I actually replaced my entire wiper mechanism because someone had put on the wrong size button where the wiper arm attaches. One button was loose when I got the car, and had been crudely drilled for a set screw. The other one was brazed (welded) onto the shaft.

Ideally, start with your wipers parked. Otherwise, you'll have to re-align everything later.

Use a tool like the 45 degree needle nose pliers to slide the wiper arm off the knurled shaft.