These engines require periodic valve checks and adjustments, or they eat the valves and seats. You can do the check without taking the camshafts out. You should do it right away. If the clearance gets to tight, you will be doing a head rebuild job. Not the end of the world, but not an afternoon project. I have done three now. Only one because of a problem with the valves. One due to a faulty thermostat and an overheating incident, and one because the head had to come off to get the front cover off. Believe me the valve adjustment is much easier. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)