Like others have noted, this era MB and model has some known warts. Insist on seeing the repair/service history before buying. Insist on a compression test. The valve stem seals are a known item and at that mileage I cannot believe they have not been changed. It was such an issue (rubber compound was not up to snuff on these and the 190E 2.3, 2.3-16 and other engines) MB developed a procedure to change the seals without removing the head. It was pretty inexpensive (under $200 for a 3.0 liter six) for my car at an independent dealer.

I think there are other issues as well. The head gaskets have a similar record of weakness, as does the oil seal around the chainbox to head/block at the front of the engine. Look for oil leaks here, and look to see if the head gasket has been replaced. Signs of a leaker would also be oil seeping out on the block, and any real issues with a well maintained car's compression. Which leads me back to the real question: What is the compression for each cylinder? Look into this and make sure you get a thorough compression test done. Dry, wet and a leakdown test if there is any sign of wear or lost compression. I had mine done before I bought the car from a private seller, at the local MB dealer and it cost me $100. Results were near perfect and I have had none of these issues in the nearly 70,000 miles I have put on the car since. Yes, it has needed an exhaust (Timevalve system) and a battery (Optima RedTop replaced a 9 year old Sears Die Hard in the last week) and the rubber in the rear suspension changed. It needs shocks and has new engine mounts as well as a window regulator for the passenger side front. But none of that should be unexpected for a 16 year old car.

Do what you need to do to convince yourself the car is solid. I think a dealer asking price of $4,000 is a good point to negotiate from, and I would rather have the known issues fixed and pay $4,000 with a one year warranty on the fixes than get the car with known issues and no warranty for $3500 or less. It is up to you, but be aware of the potential problems, especially the A/C if it is really important to you. Good luck, 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)