Originally Posted by Fidens

"I reccomend you use whatever weight of oil that your manual indicates. The engineers at Mercedes intended these engines to use this oil, using synthetic substitutes on non-completly rebuilt engines usually causes more problems than anything. To be more specific, the synthetic oil acts like a solvent. Freeing years of built up oil deposits, deposits that prevent oil from leaking out of ancient gaskets. This more slippery oil, often slips its way past piston rings and past valve guides, past gaskets and makes what was a previously well running engine into a basket case."