Sorry for the late reply, had other issues.
Well, we were heading out, in the E-Class, one winter evening 4 years ago to visit a relative and I was doing about 70 on a dual carriageway. As I crested a rise in the road I ran over something substantial lying on the road, which I didn't see till it was too late. I think it was a steel foot from the prop-leg of an articulated lorry, but can't be certain. The result was two badly buckled N/S alloys, ruined tyres (although to be fair the run flats didn't fail catastrophically and probably saved us from a very serious accident).
A phone call to the insurance for the claim, who wanted me to use their approved repairer, but I insisted on going to Mercedes Benz, because I thought they would be the best, how wrong can you be?
Two new rims were ordered, a 19"x 8.5" for the 245/40 front tyre and a 19"x 9.5" for the 275/35 rear tyre. Unfortunately for us the idiot tasked with fitting the new tyres to the rims stretched the 275 tyre on the narrow 8.5" rim and the 245 tyre on the 9.5" rim. They tracked the car as well, which must have given an interesting set up.
Upon driving the car I new it wasn't right, the handling was terrible and small bumps and potholes would unsettle the car and send the rear into a hop.
I contacted M-B and asked them to take another look, I was convinced they must have missed some more damage like a bent suspension link or damper, but said no, nothing wrong. The car went into the engine workshop for a service, during which the mechanic videos some points about the car, a buckled front N/S wheel was one issue pointed out, and uneven tyre wear was another. Again I pointed out that there must be something wrong from the original accident that had been missed, but no, they said everything was okay, probably just tracking. By this time I felt like I was banging my head against the wall.
As we had the car serviced at M-B we received a free first MOT, which we subsequently received, this again pointed out the buckled front N/S wheel, and very uneven tyre wear, but they said it was probably just the tracking out.
Yes, I could kick myself now for not noticing the mistake they made, can't believe I didn't get my hands dirty and investigate.
Skip forward a few weeks and we went out late on a Sunday afternoon in the E-Class, I immediately noticed a loud ticking sound, we had picked up a large bolt in the middle of the front N/S tyre, but the tyre was still at pressure and drivable, slowly. A phone call to Kwik-Fit, they would stay open for us and repair/replace the tyre. Upon arrival the young tyre fitter immediately asked; Why have we got the wrong size tyres fitted to the front and rear of the car?
Suddenly everything fell into place, and steam started coming out of my ears.
Long story short, I wiped the floor with them, M-B Cheshire Oaks put the entire blame on their body shop, which is VW Inchcape on Sealand Road, Chester.
We had 2x new alloys, 4x new tyres, and subsequent tracking problems revealed the suspension/wheel carrier was damaged, and all replaced.
I don't know how much this debacle cost them but it was thousands.
Anyway the LC has been diagnosed at Toyota and it is the fuel injector on cylinder 3, Error code P0203, it gets replaced soon under warranty, so I'll keep you posted on progress.
I removed the strange black plug from the OBD socket and hid it up in the dash. I noticed it has a label on it, saying something about ON for auxiliary equipment, not sure what that's about but I'm leaving well alone for now, using my spare car till the LC is fixed.
Thanks for all the help/suggestions.