This got fixed yesterday, handily* I suddenly felt like shit Thursday lunchtime and threw up several times at work so got to go home... So did it yesterday morning.
This was my 'get it working' repair
Some suitable wire was procured
And I chopped nearly all the wires back to inside the car bar the thick brown one and the speaker cables.
I spent an hour performing my best soldering
And my best heatshrinking
And before long had the loom rebuilt. Some old cable from a dyson dc25 spinal cord was used for the thick red and brown lead as I figured 240v wire would happily take the full 12v feed, the thinner wires are signal wires I think for various systems
I then wrapped the loom in tape
And fed it back through the car into the door, and taped the rubber cover back on. No idea how long it'll last, should be a fair while but now I know to just pull the whole loom back through the car if it goes again, doing it again shouldn't be the end of the world. Its got to be as good as the official repair part which is just a new plug and lots of wires that need crimping onto the car loom!
I then took the chance to fix the door card, the glue has failed that sticks the card to the mounting top plate
So I affected a seamless repair
Job done! I had a vacuum out to clear up the mountain of stripped wire ends and such from the footwell, so spent an hour shovelling the thing out, and re set up the radio from when the speaker on that door was unplugged a year ago when this issue first started and caused the headunit to stop working!
Job jobbed (for now), I can have my Laguna back. Should probably get hold of a 25a fuse to replace the 30a one used for the central locking, although I can't imagine 5a making much difference... One day! Just need to tighten the live battery terminal back down as I couldn't find my socket set yesterday, it seems happy enough just sat on the battery terminal though, the little cover keeps it pushed down