I worked on this today. First, removed the door outerskin so I could pull the rubber boot into the door to better inspect the door to pillar loom where it kinks. All looked very good indeed, I guess being the passenger door it receives less wear and tear (not the story on the tailgate loom for another thread).
The ebay lock mech currently fitted couldn't even be manually locked using the red plastic knob which wasn't activating smoothly and travelling fully. Upon removal I split the mech open and there appeared to be a peg broken on the follower of one of the spiral shafts. Interestingly, this Ebay one did have the two DC motors per VAG version unlike the recent Eby one I returned. These Chinese clones are very cheaply made inside compared to VAG original.
I still had my original VAG unit which I believed to be faulty, I've since split this open, tested the motors, joints and tracks which all seemed good. I decided to refit this and so far is working, locking, setting the alarm, locking when drive away etc.
So I've made progress but don't understand the cause of the original problem that made me replace the VAG unit a few years ago, if memory serves it wouldn't open from inside with engine running.
Removing the doorskin on 3 door car is very tight at the bottom front, I must be missing a trick as struggle to remove then refit it with door in fully open position.