Make sure the filler cap is secure. Replace the PCV valve and if the leak persists, grab a new VC gasket. Fel-Pro manufactures a gasket for the B18A1 and it sells in most shops for around 25 to 28 dollars. Clean the underside of the valve cover in the trough in which the gasket fits and also where the gasket goes flush with the top surface of the cylinder head. Try to get it spotless. If you end up having to do this, make sure that the VC bolts are torqued to about 7 ft-lbs and in the correct tightening pattern (i don't know what the CORRECT pattern is but when I replaced my VC gasket I used some pattern) Also, as it happens on my car, check the underside of the little black cap at the the end of the camshaft next to the distributor. See if there is a droplet of oil on there.
I have a feeling that someone will tell me i don't know what im talking about.