Date registered: Mar 2005
Vehicle: '01-E320 & 02-ST2
Location: John 15:18-19
Mentioned: 0 Post(s)
Quoted: 35 Post(s)
Of course you're going with synthetic: that's what MB specifies for your engine.
However, you're really asking the wrong question. Viscosity is irrelevant. What you want to be sure about is that the oil meets MB spec 229.5. The easiest oil to find that meets that spec in the US is Mobil1 0W40. That works whether you have 11K, 111K or 211K on the engine, and regardless whether you live in the middle of Death Valley or Siberia.
Other options may be found in the official spec sheet, the link for which you'll find in the W210 forum help/DIY stickies. That forum is also specific to you car, as opposed to this general one which as the name implies is more focused on topics of general interest across all model lines and years.
Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy; its inherent virtue is the equal sharing of misery. (Winston Churchill)