My advice? Call them. Your best answer is but a phone call away.
Supposedly, all MB dealers are supposed to give a discount. This is not REQUIRED, but it is a recommendation of DaimlerChrysler USA.
Star Motors here in Miami is supposed to do this. When we had an event at this dealership several months ago, I decided to pick up some hydraulic suspension fluid there, and asked for the discount.
The guy at the parts desk said he had never heard of a discount and that the guy he would have to talk to was out to lunch. We have over 100 members in our chapter, and we go to Star once per year, and yet Star's parts guy has apparently never been informed of our existence or discount.
So, rather than wait an hour or two to perhaps save a couple of dollars, I just left and bought it at Finish Line, the local indy supply shop.
It probably isn't worth the trouble to go to the dealer unless you have to. There are some discount dealers (Caliber Motors is one) that might be worth the trouble.
If you DO have to buy from them, call first, and if they tell you they DO give a discount, get the name of the guy who promised it, write it down and perhaps call again before you leave the house.
Recent supporting evidence of above allegation that MB Dealer might not be best choice:
Price for a left front window motor at MB dealer: $229.00
Price for same motor, made in Germany by Bosch at Finish Line: $71.00.
Both prices in US dollars.
Both plus 7% FL tax.
Best wishes in getting the parts you need at a good price.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"