My M116 is still so tight that it doesn't leak a drop or lose a drop of oil between 5-6k mile changes....same comes out as goes in. And I don't drive it gently.
I did a lot of "age maintenance" on it last June, dismantled the entire intake, replaced ALL rubber hoses and pieces, new injectors, spark plugs, wires etc...has run flawlessly since. Idles at 550rpm nice and smooth.
That is probably the biggest poor-running culprit of M116 or M117 engines (and the M102/103) is dried out rubber pieces causing vac leaks everywhere...then they run terrible.
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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)