I've found that Mercedes Benz NA has never been very interested in providing a good customer satisfaction experience and their dealerships, which are independently operated, only see service as a way to make $$$$$.
Find a good independent mechanic and you will be much happier and save lots of $$$$$.
If you need help to find one in your area, post a note on one of the MB discussion forums.
I do some of the work myself on my 2001 CLK320 cabrio and buying exactly the same parts online, vs dealer, saves at least 50%. All the rest is done by an independent repair shop the specializes in MB, BMW etc..