Tom,

In short:

The 300SDL is a great car, plenty of room, smooth quiet engine and plenty of power. Electricals are the same as other W126 cars so read reliable. The OM603 engine in the SDL is very robust, not quite so as the OM617 5-cylinder in the SD however. It pretty much all boils down to which car you like driving better. I will say that from experience, the 5-cylinder has less trouble with oil consumption and cylinder head problems because it is all cast iron, rather than aluminum and iron. That SD you speak of does indeed sound like a steal and at 256K has a lot more life left in it if kept maintained. Watch the tranny however, because they rarely last as long as the engines but that applies to other diesels as well. My '83 300SD rolled 263K the other day on the way back from Cleveland and still lights up in negative temperatures without being plugged in. Doesn't use any oil between 3K changes with Agip 10W-40 dino oil. This week she's receiving a transmission fluid and filter change (exactly at the 30K interval now).

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Regards,
Aaron