I followed the door latch removal steps I found here - whoops, not allowed to post it, search for 'Door lock repair'

Then removed the micro-switch and used the Dremel (1) to cut off the locating/fastening part (2) to graft onto my new micro-switch (3). I used epoxy to secure it and then adjusted the micro-switch 'clip' (4) to ensure it was held tight onto the door latch assembly. Photo (5) is the adapted new micro-switch ready prior to assembly.

Door works great and no error messages - so far.

With my new knowledge of striping the door and latch down I moved onto the rear door as this had decided it would not unlock from the outside - so clearly a problem lurking. I found that the latch circuit board had two dry joints ('cold joints') - hopefully you can see in the photos (10) (11) - zoom if you can and look at the dark ring around the joints - right in the centre, 6 joints - its the left 2 that are faulty. I soldered these up and the repair was complete without issues.

 

Here are the photos of the rear door circuit board...

And for some clarity I've added some pictures of the lock itself and the original micro-switch that was faulty.