it's from the PVC system... when N/A, the intake plenum is operating at a vacuum and this oil doesn't seep out anywhere, it's burned off by the engine. when boosted, the intake plenum is at positive pressure and this crap seeps out.

install a catch can and it will go away.

 

Then why are N/A cars getting the grime as well? Can you explain what exactly a catch can does?

Here are the pics...

 

all the grime on your pics looks to be inside the plenum, it doesn't look like it was seeping out at the gasket.

http://www.misterfixit.com/pcvvalve.htm

all that gunk that the PCV valve routes into the plenum is sucked into the engine and burned on a N/A car. it still builds up a little bit on the inside of the plenum because it's oily.

when the plenum is pressurized in a FI car, the oil and sludge can somewhat easily seep through the plenum gasket.

a catch can is basically a can or small tank that is plumbed into hoses going from the PCV valve and the plenum, with it's fittings on the top. it catches the sludge and holds it rather than routing it into the plenum for the engine to burn. you will also get a somewhat cleaner burning engine as a result.

 

No grime seeping out? Have you seen the first two pictures at the top? Thanks for the info about the catch can....has any other G/Z owner ran into this?

 

i did look at the first two pics at the top. those are yours right? and your car is boosted right?

did you get that grime on the outside of the plenum before it was boosted? it's always going to build-up on the inside.

what i'm saying is this... boosting a n/a car means that an intake plenum that is designed to operate at a vacuum is now operating under positive pressure. that is why i think your boosted g35 is getting grime built up around the plenum.