i remember seeing somthing about this posted before, maybe not your exact problems, but something to that extent...
first off let me give you my opinion of MB of Sac, they are down right rude, and when i took my car there for service they seemed incompetent with their work, and unknowledge. hence i do not bring my car there...
you're from elk grove right? well i know it is a haul but you could check out Stead Motors in Walnut Creek, they are very courtious and knowledge, you wont be treated like you would be at a lexus dealer but it was the best damn service i have received from MB, the parts/service guy i dealt with, (i could be wrong) was steve, he was knowledgable about the 202 because his wife owns one, and for sales i deal with (again i could be wrong) Jim who has been with MB for 20+ years.
again in my opinion, keep brining it in to the dealer until it is fixed as long as it is covered under warrenty that what it is for
Alex