'01 Corolla PDL Problem

2001 Toyota Corolla CE Auto 4cyl. The power door locks work fine in terms of the buttons on the remote and the buttons on the door doing their job however the lock on the driver's side door tries to go up and down but doesn't seem to have the power and I have to manually push it up or down to lock/unlock. There doesn't seem to be any unusual amount of resistance when I push it by hand so I don't think anything has jammed it up. It also works fine when I turn the key in the lock to manually lock/unlock that door. Any ideas how to fix this?

Thanks for any help.