Adding new oil helps, for a bit. The gaskets that leak, or pop out in my case, are paper gaskets so the high mileage oil doesn't really help with that. Here's a link to an image of what mine looks like. It's right next to the left side hole where the cams come through the rear case. I was working on a noise problem when I found it. My right head has a crack in it so I'm replacing it. The cams and lifters on that side look like new. I just pulled the left side rocker cover off, which is the side the gasket popped out, and the cams are burned pretty badly. Lots of scoring and worn lifter tops. It definitely shows there was a lubrication issue. There is about 1/2" of gasket missing from the gallery. It's probably in the oil pan ready to clog something up. Who uses paper gaskets anymore, besides Nissan?
Picture:
http://photos.google.com/share/AF1QipNc ... ZiMXRYSWx3