I believe they are like all other M112 V6's and are supposed to run on platinum plugs.
Gillybenztech moderates the ML, G-wagen, and Unimog forum, and I would probably repost this over there.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".