Welcome to the LEF.
You could start by taking off the inlet manifold, and looking down the inlet ports to see if oil is present. This is a possible cause of your problem, but I am skeptical as the PH engine has an internal breather pipe from the inlet port (which sucks oil mist directly into the inlet port, hence preventing oil been sucked down the inlet guide, you will see what I mean if you take off one of the rocker covers)
However, it is more likely to be oil control ring wear or if the oil control rings have stuck in the grooves. Might be time to go for a top end overhaul? as parts are still easy to find to find for the PH.
If you prefer genuine parts google the Jim Perkins and he can supply you with genuine OEM parts.