Anytime you remove the engine cover on a G37 or 370z, make sure the center bolt's metal insert (or top hat) is in place. This prevents the bolt from being screwed in too far and puncturing a hole in your intake manifold.
If yours is missing, here is a quick check to see if you have punctured a hole into the plastic intake manifold:
Start the car with the cover off and place your finger over the center brass insert on the intake manifold. If you feel any suction, you have poked a hole into it.
A replacement insert can be purchased from the dealer. Infiniti calls it a "Engine Cover Sleeve", part number 16566-JK20A. The are about $8 each.
On re-assembly, add a little thread lock (Loctite 242/Blue) to the center bolt when reassembling.
From now on, anytime you remove the cover, ALWAYS have a quick check to make sure all the sleeves are in place and you won't poke a hole into your intake manifold... which is a good thing :)
