Plan on a valve job every 250,000 miles or so, MB doesn't use stellited valve on the 617 and the exhaust valves will get worn badly enough by then to leak.

Bottom end should go 500,000 without repairs, at which point the rings are usually leaking enough to cause trouble.

Ditto for the gas engines, by the way, except that the rings should last longer in the aluminum blocks.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!