Had the door lining off and took a good look round over the w/e.
All the wiring looks sound. Seems well protected especially in the door pillar/hinge area.
After a lot of arsing around I think it may be that the connecting rod linking the lock to the latch mechanism is slightly too long (they are adjustable) and wasn't pulling the activating plunger thing on the C/L unit far enough to trigger it every time.
I shortened the con-rod a little and it has all been fine since.
Of course as soon as I relax and replace the door trim it'll stop working again
