I purchased my 83 300D (131,000 miles) in Seattle on Sept 04 for $3000. The lady was asking $4000 but I doubt that she realized what she had. Even though you say it is "mint", I'd have a independent shop look at the transmission, the engine compression, the vacuum system, and the climate control system. I also place great value on the condition of the body (lack of rust, paint condition, etc.) the interior (no dashboard cracks, and the upholstery in perfect condition), and the presence of all the original equipment like the radio, original owners manual, tool kit, etc.. I feel that one can always find a good deal out there if you are patient. I also bought my 85 300SD (101k miles) one month ago for $4500 (asking price was $4950). This car is what I'd consider "mint". Subject to the car passing all the inspection points and if the condition is excellent, I'd offer $4000 and walk if it's not accepted. Then again, older car values are based on what you are willing to pay and how bad you want the car. Check my recent thread entitled "My Stable" for an example of what kind of cars can be found when you are patient. Good Luck.

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1983 M-B 300D, 148K, daughter's ride
1983 M-B 300TD, 120K, my ride
1985 M-B 300SD, 102K, wife's ride
1969 HD FLH, 45K, restored/hobby
1996 Chev Suburban, family taxi/tow vehicle
1990 John Deere Model 240
1942 John Deere Model LA
1985 16' 4Winns ski boat