Hi Folks

My query relates to positive crankcase pressure on a ’92 940 2.3 non turbo 8 valve. I’ve read through the ‘700/900 Maintenance FAQ’ but would appreciate some specific advice on this problem if anybody can help.
It started around a month ago with oil leaking from the filler cap. I proceeded to check the PCV system over and found the hose to the manifold disconnected and blocked as well as the flame trap being only partially clear. Cleaning and reconnecting these items improved things noticeably but the leak persisted albeit at a reduced rate. I then replaced the ‘breather box’ and filler cap ‘O’ ring and the leak was reduced to a growing smear on the rocker cover around the filler cap.
For information, the engine has covered 160,000 miles still pulls like a train and does not use any water or oil to speak of. The leak is only noticeable when running at high load and RPM – the car is used on motorways regularly.
My query is, where do I go from here in terms of troubleshooting and rectification? Do I need to refer this to my Volvo specialist, or are there steps I can/ should take now? Moreover, do I need to worry about blowing main gaskets out?
Many Thanks in advance.