I have a 1998 V70 GLX, there is a cover over the spark plugs, when you add oil, it will get under and sit on top of hot engine, remove and clean oil and keepit clean

 

It could be something as simple as a bad gasket under the oil fill cap or it could be that you're due for a PCV system replacement. You might have some backpressure in the engine from the PCV being slightly clogged that is pushing the oil out from under the oil fill cap.