When I bought my car, the guy thought the turbo was f**ked, blew HEAPS of smoke on boost.. he had the breather hoses set up wrong..
The PCV is a little plastic valve on the outside of the intake cam cover, it connects via a hose to the intake manifold and allows the crankcase to ventilate when the engine is under vaccum but stops the crankcase from pressurising when on boost. It *could* be getting stuck open intermittently I guess.. allowing the crankcase to pressurise and blow some oil past the rings..
When it does happen, is it after a little boot? or completely random?