You can check blow-by by taking the oil filler cap off while the engine is running and place it over the opening. A general rule of thumb is if it stays put, blow-by is insignificant, if the cap gets blown of or moves around a lot, you've got low compression somewhere (which apparently causes lower combustion). Also, blue smoke means oil is being burned, not black.

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition