All - After much research on this as always helpful forum and an afternoon of fiddling with the inner realms of the drivers door, I successfully removed the door locking mechanism, soldered a suspect dry joint and refitted. All seemed to be working properly. . . . .however, although the car now recognises when the drivers door is open (i.e. courtesy light comes on, display on dash illustrates door open and headlight warning buzzer now works again) . . . . the bizarre central locking problems still happen.

Symptoms: Car will not unlock at all on unlocking with the keyfob unless, you press the lock button twice (i.e. to disable deadlocks and internal monitoring), then press unlock once. The car doors and boot then unlock then lock straight away (you can open the door if you grab it for the fraction of a second it is actually unlocked!).

However . . . . if the boot is open, everything appears to work absolutely fine!

So the question - I was about to start trying to fiddle about with the CCU (which by my research on here is behind the light dial on the dash somewhere?), but was wondering if there is a "dismantle, clean and potentially resolder" the boot locking mechanism, particularly around any switches lurking in there. If so are there any handy photos lurking on the forum somewhere in the same way as there are for the Drivers mechanism? (Apologies if it is obviously on here somewhere but I'll be b&*ggered if I can find it!)

As an aside, I have ordered a cheapy fleabay vagcom lead and am awaiting that to see if any coding issues can shed any light.

Hoorah! Think I've finally found the problem, after restripping the door innards out and giving the driver's door mechanism the once over again all as it turns out completely unnecessary! (by the way I recommend a good squirt of WD40 on the actual switch buttons inside the locking mechanism if you ever dismantle it, 'cos the one controlling the door open switch - the one with two wires to it from memory - was a bit sticky I had thought it was dry joints but even after resoldering it stopped again, WD40 seems to have fixed it, and courtesy light and headlight warning buzzer now working again).

Anyway, cheapy vagcom lead arrived in the post, and using shareware vagcom 409.1 it mentioned an intermittent short to ground on the tailgate. Thought I'd have a quick look at the rear end of the car only to discover the best part of the contents of the screen wash reservoir sloshing around under the CD multichanger right around those 3 electrical connecting blocks. Looks like it's been there a while fair bit of corrosion on the connections, dried with hairdryer and had to snip a couple and bypass wire them ('cos the connecting pins were completely mullered) - and hopefully everything is OK.

The culprit is the tube carrying the screen wash to the rear window. Not sure if standard but on my car there is a very inconvenient plastic connector in the (approx 8mm) black tubing held together with a small hose clip. Looks like mine has been leaking for a while, so gave it a bit of a clean and tightened the hose clip, will wrap a load of amalgamating tape round it when I get a mo.

Sorry for all the text, but if you're searching this forum (like I did for an age) 'cos you're having locking problems I hadn't seen any reference to checking the bottom of the CD multichanger compartment. And for those without a multichanger it's the compartment on the passenger side of the boot just nehind the wheel arch. So check that aswell as the other areas already mentioned in other threads!