I'm having massive dramas with the central locking on the rear passenger side door of my Discovery 1. I have changed the actuator, it will only open the door but will not lock it again. I can lock it manually and the actuator will open it again. The linkage is well lubricated and when disconnected from the lock moves freely without any resistance in both directions. I changed the Spring on the lock catch today but still no luck. I'm running out of ideas on what it could be. Any help would be greatly appreciated.

Readjust the actuators mounting plate one way or the other slightly only a millimetre or two until u have both locking/unlocking, testing after each time u move the plate. Simples.