By burning oil, do you mean you had to start adding oil or that you started getting blue smoke?

If the plug hole is leaking, it needs a Helicoil or Timesert inlet, the threads are bad (from overtightening the spark plugs or not using ant-sieze on them).

A plug suddenly getting oily like that could mean a valve guide loose in the head, or it could mean a bad plug wire so it never fires, leaving oily gasoline resdiue on it, or a plugged fuel injector so that no fuel ever reached that cylinder. Any of these would give you a dead miss on that cylinder, too.

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!