Zafira B Drivers side rear door won't Lock?

Vauxhall Zafira B 1.6 on a 55 Plate.
Driver rear passenger door will not lock.
Was intermittent, now constant. Looked at the maunual, no help at all. Sync'd the key, no success. Checked fuses, only 1 a 25A is ok pulled out plug from door and that seems ok too. I can hear a noise from the lock when i try and lock it and can feel a vibration so something is trying to work ruling out wiring fault to lock motors. And Ideas b4 I spend a fortune in a garage??? :-(