Well, it is true from mobil1's website that it says that they do ship Mercedes-Benz cars from the factory with mobil 1 now. (I wonder what they used before?). I have read alot about synthetics, and it seems that they do better in extreme weather climates, but if your climate is not that extreme, you could use any oil.? true? All I want is the BEST oil for my car, thats all, if every one says synthetic, and it wont hurt (and hopefully help) an existing older engine, then I will do it. I feel awful putting in such a cheap oil (rotella). So, if I am a quart low, could I just put in a quart of sythetic (along with the rotella multigrade?)would that hurt it?..or do I just change everything over to synthetic with my next oil change?..thanks