Valve guide seals definitely, and check the oil filler gasket. A leak here only shows up at speed, engine usually doesn't drip much in the drive. Can cause oil usage of upward of a quart in 1000 miles all by itself. Add bad seals and leaking valve cover gaskets, and you are up to a quart in 500.

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!