Here's the deal on Mobil 1 oil:
In model year 2000, the maintenance is included (paid for by MB) during the warranty period (4 years/50,000 miles). Per MB, when performing the maintenance services on these cars while still under factory warranty, we are to use synthetic oil. Preferred is Mobil1 0W40, but there is a short list of other approved oil brands. Once the car is out of warranty, it's up to the owner to decide what to use, period. If the dealership takes it upon themselves to mandate to the owner what they will use for oil, and the owner is willing to allow this to happen, and everyone is happy about that, well.....fine.
MB did send out a notice to other MB owners as well about switching to synthetic, I am unsure if this is only to owners of the vehicles of 1998 and 1999 with the modular V6 and V8 engines or exactly who got these letters, but I do know MB wants synthetic ran in these engines in the worst way, but they aren't paying for it, except in the 2000 on up that are still under warranty.