Oil on valve covers

Two things - the reason breather filters (those are the factory breather with the big nipple on it) go to the air clraner on stock systems is because that is a source of cleaner air. Nothing to do with pressure. All it means if it's not connected its that you might want to replace it every 2-3 times you replace or clean the open element air filter.
Now - the ones you see for sale now many times have the hole under the filter element as a partially punched hole. Pull the breather out, adn look into the bottom that goes into the valve cover... If you have one that's punched in a semi-circle and slightly bent in to allow air flow, make sure when you reinstall it that the uncut side of the semicircle is oriented "up", or towards the air cleaner - not nearest the exhaust manifold/header. On really troublesome ones I'll make a mark on the breather so I know where that uncut area is. Because the oil vapor condenses in the breather when blowby overcomes the PCV suction, the condensed oil drips over the non-punched section, and drips out the exterior holes. If the cut side of the semi-circle is down, the oil will drip back into the valve cover assuming the blow by is within normal amounts.
If the blowby is more than it should be, there's nothing to do but wipe it off.