What year is it? There is no such thing as a 1985 300SDL. Its either a 1985 300SD with a 617, or a 1986 300SDL with a 603. Different animals.

Lets for now assume its a 603. The vac pump probably let go, I'd certainly pull the head and see what is going on. For a proper fix figure a long block to the tune of about $6k-$7k. Used engines with a million miles on them can be found with a lot of searching for $1k-$2k.

I would only repower an SDL if the car was real cherry, it would have to be a real show car to be worth the money. Or like your dads favorite car before he died or something like that. I would also never consider installing a used engine but thats just me. Remain or new long block is the only way I would consider going.

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