I spoke with mbusa today on the phone. The guy was very indifferent to my problem and was borderline rude.
I told him about my problems with the wiring harness, that it seems to be quite a common problem, and even read the safety recall, the TSB number and the issue date.
He pretended to have no idea what I was talking about, stated that Mercedes has never issued a safety recall regarding the wiring harness, and didn't even know what a TSB is.
He stated that I could go to a dealer and plead my case, but that it would be up to them and they would take into consideration whether or not I had bought the car from them, service history, etc. I suppose that if I was a customer of a specific dealer, i.e. bought the car (new or used) from them, serviced it from them, they would probably be inclined to help me in order to keep a good customer.
But since I didn't buy the car from them and have never had the car serviced by them, I have little confidence they'll help me out.
I'll give it a shot, though, but I'm dreading it...