911 Turbo w/ oil in the intake
 

I have a 2002 911 turbo w/ a check engine light on (but no DTC's stored) and oil collecting in the intake hoses and air intake distributor. I discovered a faulty check valve at the back-center of the air distributor and replaced it, which fixed the problem for a couple of weeks. Now the oil is back and the check valve seems to be working correctly. Anybody know about checking all of the other valves? Anyone had a similar problem?
Thanks much.