...maybe you should ask your dealer instead of searching the Internet! People should know that there is a lot of wrong information on the Internet.
Our computers are linked with DCAG (DaimlerChrysler AG Germany)
Your car is a ML320, the engine code is 112.942, recommended oil types are on sheet 229.1, recommended viscosities are on 224.1.
When I look at my computer at the ORIGINAL MB 229.1 sheet (full name: BB00.40-P-0229-01A), I see following recommended MOBIL oils: 1 Tri-synthetic; Delvac CX; Delvac MX (only 15W40); Special S; Special X; Super F-XHP; Super Formula; Super M; Super S; Super S Diesel; Super XHP; Universal FL.
When I look at the ORIGINAL MB 224.1 sheet (full name: BB00.40-P-0224-01A), I see following recommended viscosities: all temperatures: 0W30; 5W30; 0W40; 5W40; 5W50, temperatures above -4° (-20°C): 10W30; 10W40; 10W50; 10W60, temperatures above 5° (-15°C): 15W40; 15W50, temperatures above 23° (-5°C): 20W40; 20W50.
This is the information from DCAG, but maybe that website has "special information"...or MBUSA has "own" 229.1-sheets?
Or maybe you should just ask MBUSA if they have specific standards instead of those from DCAG?
...But do not use non-MB-information!