That is incorrect. They come prefilled from the factory with a 10W-40 synthetic blend (factory special prefill). Any ACEA A3/B3 oil will due from then on (I prefer Mobil 1 15W-50). I was not aware that they now mandate Mobil 1. Only cars that come prefilled with Mobil 1 are the AMG cars.
ALSO, NEVER CHANGE FACTORY FILL UNTIL AT LEAST 4,000 MILES! It's a special fill and filter for break-in. If you do, your car may not break in until higher mileages.
1988 Mercedes-Benz 260E