I'd say it's most likely one or both of your exhaust manifiold's, I believe the most common side to go on the VG30 was the driver side. They had the same issue on the Maxima engines, same manifold issue.
I worked for Nissan for a few years and I did countless amount of these manifolds, it was easy money, warranty work.
It could be the bolts, the manifold is warped or the manifold itself could be cracked in half, I pulled a lot of them out in two pieces once I got the bolts out.
On the VG30, which you have, it was a lot harder of a job as the bolts would tend to break inside the head and you'd havde to drill them out. At the time I worked for Nissan we were seeing a lot more of them on the VG33 which is the Pathy's from 96-99. They were easier as the bolts would usually always come out no problem, the problem with them was the actual manifold's themselves would warp and/or crack. But I did see a decent amount of warped and/or cracked VG30 manifolds.
RTV won't do a thing, exhaust manifolds are extremely hot and will melt RTV right away. More than likely you won't be able to see where it's leaking anyway or be able to get to it too easy.
At most it will just be an annoying noise, but you may see some worse gas mileage than expected, as the O2 sensor isn't gonna get an accurate reading. Depending on the state you live in, it could cause you to fail inspection also. In NY that would fail as soon as it came in the door.
Just for the hell of it you might want to check with Nissan and see if they may possibly still goodwill it, you never know. Check a couple of different dealers.