Vaccuum pressure in top of engine

I have replaced the pcv filter. there is still air pressure build up and oil drips from under the oil filler cap. I am affraid if i replace the oil filler cap to get a tight seal that the pressure will blow the oil out somewhere else. Do you know what could be causing the pressure build up? asside from the pcv filter, do I need to be sure there isn’t a clog in another location of the pcv system? if so, can you tell me where this clog might typically be located?

Yes…Where the PCV vacuum hose connects to its source on the intake manifold. This fitting can become clogged up. Remove the hose from this point and you should have STRONG flow at this fitting…Year, make, model, mileage??

The engine crankcase and the space under the valve cover can become pressurized by blow-by past the piston rings. If the hose (or, pipe) that leads to the pcv port on the engine intake manifold is plugged, the crankcase pressure has no place to go except out the oil dipstick hole, or the oil cap, or force its way out somewhere else. If there is a LOT of blow-by, it might be too much for the pcv to handle. At worse, the engine could need a ring job.
You replaced the pcv valve? You need to ensure the hose/pipe to the crankcase is clear. A straightened wire coat hanger might do.

1995 Volvo 850, 150k miles

We did a compression test and ther does not appear to be abnormal blow-by. i replaced both hoses that connect to the engine and the PCV Valve/filter. THere was excessive sludge build-up in the port where the hose from the PCV valve mounts to the crankcase so i cleaned that sludge thoroughly. Is there another place in the PCV system that could be clogged?