'99 ML320 purchased in '98. Castrol mineral oil and filter every 5,000 miles. Gutted the cats immediately and turned off idiot light with O2 simulator. Run the cheapest gas I can find as combustion chamber temps are down w/o the EPA exhaust potatoes and the computer doesn't sense knock and detune the engine for reduced gas mileage.
Replaced crankshaft position sensor, mass air sensor, and unclogged EGR pipe; nothing important. 227,000 miles. Am installing transmission fluid temp gauge as I need to do some towing.

'13 Ml350 BT, took delivery 2 weeks ago today. Filled the tank for the first time today. Trip computer was telling me 26.2 MPG since reset (deliver day), my calculation of miles driven by gallons purchased came to 24.3 mpg. That's a number that makes me happy!