That train of thought makes sense to me, the charger pressure has leaked back through the one way valve, as it wasnt working as a valve it was basically a pipe. The pipe fed the pressurised air into the crank, with the easiest route to vent being your dipstick tube and filler cap.
I remember reading it was tapping like fuck when your oil beeper was beeping (but no oil light? Does this light work? Does it come on when the ign is set to on before cranking the engine?).
Do you have an oil pressure gauge or can you buy / borrow one from someone? I don't know what the inlet and outlet pressures should be and at what point (ie do you measure it at tickover for lowest pressure vs under full load at WOT and high rpm to reflect hardest running conditions......... this is what I would do personally, if there's nothing to compare to/ no need then don't do this). If you can fit a gauge before the charger, ideally at the charger oil inlet (as this would closely reflect the true value) and get a reading it at least gives you a starting point. I've lost my haynes manuals and don't have access to Autodata anymore, but someone else may be able to pipe up with the oil pressure specs?
Getting the oil up to temperature would affect the reading too. It'll be thicker when cold.
Have you opened the charger and looked inside?? If this is easier it may be best to do this, have a quick visual check, take pics and upload to here if you're not sure and again, someone will be able to help you.
Where are you located roughly? Could always borrow someone elses charger / stick yours on their car to test?