I'm a fan of the old blowby test,if conditions and the mood of the seller don't allow for more comprehensive examination.

Pull the cranckase hose from the air cleaner and see how much blowby is pushing thru,generally a cold motor will give you a good deal.It's an acquired skill though.

A warm engine however should give you only moderate pressure,you put yer finger over the hose opening and you should encounter little resistance,scored cylinders will also telegraph noise thru the hose end.

I have bought, sold and used a fair amount of diesels. One 300d with only 95,000miles would choke on it's own blowby after a hard run up a hill,my current 300 turbo with 210k runs as new.

By all means insist upon a compression,or better a cylinder leakdown test if the owner is willing to do this.

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