Mine has been pretty stable ever since I bought it with 92K on it. The milage hasen't changed much even though the head was reworked (camshaft, cam followers, valves, guides, seals and gasket.) I have repalced the fuel pump chack valves for hard starting. None of these changes have resulted in a change in the milage. I am still running the original rotor cap and wires @ 153K.
88 300E 225K Sold
2000 C230K Totaled @103K
2003 ML320 140K Granddaughters Limo
2009 E350 4Matic Sport 37K Sold
2011 ML350 44K