To my mind, you want the lowest mileage, rust free, 82-85 300D your circumstances allow you to purchase. I'm not talking about less than 100K, I'd personally be a little suspicious of a car like that, but something that was treated right, with 150-175K should be around for at least another 15 years if maintained. These car will last a long time, but not in a maintenance vacuum.

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1985 300D Gretchen (Astral Silver) 220k
1983 240D 4-speed Evelyn (Orient Red) 203k


TANSTAAFL