You should be using motor oil that meets Mercedes specification 229.3 or 229.5
No other numbers on the oil bottle are as important as these, and the other numbers are in fact essentially meaningless.
Oil that doesn't have the Mercedes approval printed on the bottle is not suitable.
The easiest to find conforming oil is Mobil 1 European Formula 0W-40.
Because one version of Mobil 1 meets the requirement does not in any way mean they all do.
This information is in your owners manual, and if you don't have an owners manual you can get one at your dealer or by calling 800.for.merc.
See
http://www.startekinfo.com/StarTek/outside/9511/?requestedDocId=9511