You could try and check the wiring in the rubber sleeve between the door and piller. the wires break inside so the central locking stops. had same trouble on my zafira. i just found the matching wires ( after a bit of hassle with the rubber sleeve) and extended them a bit by souldering a small piece of identical wire to the broken ones. not had trouble since. hope this helps.
darrylgibbs
June 2008