Sorry I can't answer any of your technical questions, but I will suggest that you mention what happened to your mechanic. That could have been a safety concern, and it needs to be addressed to your mechanic. You paid him to do a competent job, and you have every right to bitch if you feel the job was not up to par. I used to take my M-B to this indie M-B shop. In a nut shell, here is a list of what they did or didn't do:

1. After an oil change, they failed to securely screw the belly pan in place. Drove the car on the freeway home only to find out the pan was barely hanging on! Grrrr!

2. After a routine transmission fluid change, noticed after a few weeks that ATF was seeping from the transmission pan and spraying a light mist of ATF on my undercarriage. I found this out when I noticed my car was smoking from underneath! I went to another indie M-B shop and they said the transmission pan was not tight.

3. Ripped me off on a major brake job (all rotors, pads, and sensors replaced). Worst, they spilled brake fluid in my engine bay and somehow heavily soiled my new hood pad right above the brake fluid resevoir! They didn't even bothered to tell me. I found this out on my own. (I always do a pre and a post-inspection of my car everytime I take my car in for service.)

I was very upset on the last one. I went back and tried to express my disatisfaction. I wrote a letter and stopped going there. The place did offer to replace a new hood pad, but I declined. I did not want them to touch my car again. Keep in mind this was an indie shop specializing in BMW, Volvo, and M-B.

Remember, be fair and courteous when making a complaint. If they get all pissy about it, then it's their problem, not yours.