The crankcase breather attached to the intake manifold is intended to provide a small amount of positive (as opposed to passive I suppose) crankcase ventilation, but typically on an old Volvo engine like that it just has a very small hole that sucks a small amount of air through, and mostly at idle (there is little or no vaccum in the intake manifold with the throttle wide open). So despite the large hose there is really little flow available through that route.

If more crankcase pressure is being generated (by air leaking past the rings) then the air will flow the other way through the PCV system - going out that flame trap and through the other tube and into the intake system upstream of the throttle. That whole gizmo just bolts to the block with a single small bolt underneath and has a large O-ring for sealing. You could just take the whole thing off and soak it in some degreaser.
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