More likely worn out valve guides and a bad rotocap on the #1 exhaust. This allows the valve to "wear in" on the seat asymetrically, so that it seals at one point in rotation but doesn't at others. Common on high milage engines.

If you don't have oil consumption problems, I'd bet a good valve job will restore the engine to like new running condition.

A tight exhaust valve will act similar -- it's OK on a cold engine, but won't seal all the time warm. Crud built up on the stem will do the same thing -- it moves completely closes slowly.

Cure for that is to set the valves about 0.010 inch loose for a while a see if they close up.

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!