So the rear middle plenum bolt on my 06 z has some oil gunk sort of building up in the recess around it. That's the only one of the bunch that's having this issue. It's not loose to the point where I can spin it with my fingers, although I haven't hit it with a torque wrench.

As a side note, my car is also experiencing the (fairly common) pre-ignition/pinging/detonation issue between 2-3k RPM. Could these things be related? Is it time for a catch can?

 

catch can will never hurt.. youll have to buy one w ..or get inventive to make it baffled tho.

 

So apparently it wasn't actually oil. Turns out the gunk is greenish, isolated to the one middle rear bolt:

 

Coolant?

 

Looks that way. Question is - how did it get there?

 

Oxidised aluminium. Probably got some water in there at some point.

 

you think? there was pretty good amount of it in there, whats in the pic was just a tiny bit i scooped for the picture.

 

Maybe get a pic of the plenum upper with the problem?