All ERSTs have some oil in the intake, its the way the breather system is designed. If the rings are knackered then the crankcase pressure will be higher forcing more oil through the breather and into the inlet.

If you are spending alot of cash on rebuilding the engine then i would also get the turbo rebuilt or replaced.

You could also re-design the breather system so it doesnt feed through the intake, an alloy breather with a vent filter or piped up to a catchtank with vented cap.