This thread's a little old but I would recommend using Locas Syn Oil Additive. 0W40 is so thin that the 3.2L MB engine makes all sorts of chattering sound. You can especially here it when your'e driving a convertible Crossfire. I had a 3.0L Mitsu Eclipse that made similiar noise and 1/2 quart of Lucas Oil to each change allowed the oil to stick better to rotating engine parts. I'm either going to switch to 5W40 or use 0W40 with Lucas Oil. As for fuel additives, the best way to clean your fuel system is to suck a can of seafoam directly into the intake through a vacuum line while the car is running and it basically steam cleans your valves and seals.