The upper intake manifold has greasy residue at the gasket, similar to when the valve cover gasket is shot.
Where could that be coming from?

 

same here i think is just dirt that get trapped in that spot because i changed the gasket 3 months ago and still same thing

 

But why only along the gasket? Could it mean that there is a leak and the carbon deposited inside the IM is getting out?

 

at first i thought there was a leak and the intake was sucking dirt and some of it got trapped there

 

I actually talked to two different Nissan technician's at different times about this. They both said not to worry about it, and that it was not a leak. The second guy told me that I would difinately know if I had a leak by the way the car would react. He also told me that if I wanted to that they would change the gasket, but that it would do the same thing after a little while. I have not worried about it since, this was at least a couple of years ago.