I had the same problem (one of my door speakers was fried). I wanted to report back to you on my situation. I called Bose and the minute I mentioned Mercedes Benz, they said that I had to go to the dealer to purchase the replacement speaker. My next plan of action was to go to the Bose website and use email to "confirm" that the address was correct for ordering a part. The address I confirmed was one from this website and I think this thread the address in Stow MA. Instead of receiving confirmation on the address, I received an email response saying that I could order a part by calling 1-800-231-2673 with the part number (#171800 for the larger of the two door speakers) and a credit card number. I did this and it worked. I ordered 2 speakers and the total tab was 89.00 even. The speakers showed up in two days. This guy showed me how to get the door panel off. Mercedes R129 Door Surgery Good Luck!
I received an email response saying that I could order a part by calling 1-800-231-2673 with the part number (#171800 for the larger of the two door speakers) and a credit card number. I did this and it worked. I ordered 2 speakers and the total tab was 89.00 even. The speakers showed up in two days. This guy showed me how to get the door panel off. Mercedes R129 Door Surgery Good Luck!