I have read that 1 tablespoon of thick wheel bearing grease is used to help seal the paddle. Oil in the grease evaporates over time and the grease thickens. Over time, leather (or the paddle-to-housing material) ages out and becomes stiff and/or wears. Over time the inside of the housing can wear down. Injecting various chemicals into the motor may help the motor to function again but this may be a temporary solution i.e. the problem comes back. Also be careful of the chemicals you use because they may be sucked back into the engine and cause damage.
We all know what happens when piston rings wear out in our engines. It's time for a rebuild. It's the same for a vacuum motor. If you can stall the motor my gripping the output shaft (not the wiper arm) with your fingers, the motor needs servicing. Flicken has the parts, knowledge and experience.
One more thing, there is a piece called a rocker that is attached to a spring. If the rocker breaks (becomes brittle and snaps), the motor will operate once in one direction and stop. The rocker and other parts are used to switch direction of the motor for wiping action.
