I really dont like the way your catch can has been described to me.. If it indeed has no vacuum source (ie its not connected up to the intake manifold) this coupled with the overservice, would defiantly cause positive pressure down low. Hence volcanic irruptions out the rocker cover breather.
Either remove it (and re-connect the factory line from the PCV to the intake manifold).. or connect it up so that the return still goes to the intake manifold (ie vacuum source) with a secondary PCV or check valve in this return line to make sure the catch can noes not get boost pressure applied to it when your turbo spools.
The way your catch can has been describes is here: "Very good theory there DOC, will investigate this, the oil catch can is more than likely setup in the wrong area, cause i have noticed it is not set with an through port (It only has a hose comin in) and then is meant to vent to atmosphere through a threaded bleed nut so to speak."
Let me know how you go mate.. and I hope your on the mend too.
Doc