Crank Case Vent (CCV) vents into the turbo intake tube. Oil can accumulate in the intake and turbo and eventually leak down into the engine valley. There are a few CCV mods out there to correct that problem. Could be an oil inspection plug or the o ring gone bad on the ICP sensor. ICP sensor can also leak oil through the electrical connector, unplug it and make sure its not wet with oil. And of course the HPOP line fittings connected to your Rt and Lt heads may be leaking.