I have only had experience with 3 dealers in 3 different cities. 2 of them were slow in doing the service and did not always fix what I wanted fixed. The best was in Halifax. Great service, always washed and vacuumed the car before they gave it back, and always fixed what I wanted fixed the first time, with no problems afterwards. Not all dealers are bad, but I guess not all are good either. I would make them give you a new car. You certainly deserve it. If I were shelling out money for a new Benz, especially a top of the line model like yours, I would not expect to have to take it in until the first oil change, and I would expect to be treated like royalty by the dealer for life.
1995 E420 - retired
1986 420SEL - retired