Nice honest write up. Try to get the sls prob sorted especially if it's just a loose/damaged wire. There is a section of the loom that goes over the rear axle that is a common problem with these. Potential worst case for a sls rebuild is £800 in parts so people will think that way, if you can eradicate that possibility you will save ££s from hard negotiations.
Try to put a recent pic or two up to show YOUR car and not just 4stars:deal:
thanks for the input steve, added a couple more photos, and will get a few more up when i get the spare time.
gonna phone the garage, and get the car in, to get them to have a look around the axle area as you mentioned, to see if a loose or broken wire could be the cause maybe