I am in the process of swapping out my spark plugs and noticed that two out of the six I removed had what looks like oil residue on it. I have attached a picture of one without the residue and one with residue. Is that an indication that there is a leaky gasket in the engine? Any information and/or recommendations would be greatly appreciated.

 

I don't know if the VQ350 engine has the same o-ring arrangement between the cylinder head and the timing cover but on the KA24D series engine used in Altima and Maxima (?) that sort of oil leak is a sign that the o-ring is leaking. Easy fix on the KA2D series.

 

I had the same thing happen on my 4th gen maxima with a vq30de motor (the G35 uses the vq35de). When I pulled the plugs at 60k I found 2 of the 6 bathed in engine oil on top. The car was under warranty so I had the o rings replaced at the dealership. I wouldn't have paid to do it since it was big $$$ in labor. At 120k I pulled the plugs again and found the same 2 bathed in oil. It never gave me any problems, so I just put it back together and drove on.

 

Although I see a lot of oil on that plug, the actual electrode looks dry still. Was the actual electrode fouled or was it mostly on the external parts of the plug?

 

Yep, the valve cover O-rings have failed. Easy fix for the dealer.