You may or may not have a real problem, so don't get overly concerned. The filler cap might need a new gasket, less than $1 at the dealer to stop the leak.

Because you have an 800 mile trip planned, I have a suggestion you might want to consider. Get a bottle of AutoRx from your local auto parts store, remove enough oil from the engine to make room for the AutoRx, and take your trip. The AutoRx will clean all of the gunk from the engine AND (some report) clean the oil separator at the same time.

If you put a new gasket on your oil cap, warm up the engine and pull the dipstick out with the engine running. Check for vacuum pressure at the dipstick using a thin piece of paper. If crankcase pressure is blowing out of the dipstick at idle, your PCV system is clogged somewhere, otherwise, you are good to go.

BTW, Volvo reccomends replacing the oil filler cap gasket annually. It should be reasonably soft and pliable.

Klaus
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Praying for Cynthia Amendt, heaven bound