I bought a 1987 300TD for $12k. A lot? Yes. But, I bought it from the family of the original owner, and it was (still is) in excellent condition. It drives like a champ -- best road trip car I've ever driven. If your engine is clean & passes inspection (yours or somebody else's), then the mileage is no problem. I also own a 1982 300D with somewhere north of 350k miles on the engine, and it's completely solid. These engines will go the distance, if given the chance.

The coolant may not be spec -- it should not be green. If it is green, look for any signs of any kind of liquid on the ground under the engine after it is parked. If it's green, you will probably have to replace the water pump & then install the proper coolant (Zerex). That job is a PITA, but you van do it yourself (took me three months but cost a bit under $225 in parts, including tools & antifreeze, as well as water pump, water pump housing, thermostat, gaskets, etc.).

I run synthetic Mobil 1 15w50 in mine. If you're going to run WVO in yours, or even biodiesel, you should use the same oil in yours. Synthetic works better with veggie oil/biodiesel than does dino oil.

I passed on a couple of 300TDs in the $6k to $7k range to buy mine for a lot more -- because they either had body damage or didn't drive right. If yours has a perfect body, perfect interior and drivers perfectly, buy it and don't look back. You won't regret it.

cheers,
~Garlynn