Get it rebuilt at Fickens, or buy a new or rebuilt wiper motor.
Cleaning and lubricating a vacuum wiper motor might help but most often it needs to be rebuilt (parts that wear need to be replaced).
A dual-action pump should help but I have had bad luck after receiving a few dual-action pumps that had dried-out on the shelf or had been poorly rebuilt (I'll send them to be rebuilt by Fickens before buying another new or "rebuilt/remanufactured/reconditioned" one).
