My sister's '87 300D has that problem. Oil level was full.

However my sister was panicking in the car that it was going to break down and die, or maybe she'd ruin the engine. EVEN AFTER I checked it, and I told her it was FINE.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)