Sounds like you have a bad actuator in the driver's side door. Easy replacement.

Just be careful taking off the door card; it has plastic L shaped retainers in the door card that will break. You must slide the door card up and then pull it off the door frame - otherwise you risk breaking the plastic retainers.

Think I paid between $25-50 for actuators maybe five to ten years ago when I replaced two on my 300 SD.