Even though it is two years after you posted this, I will tell you that it is done over here in Peru, they use same type of seal that fits in a Nissan but with a type of epoxy, they mix those two materials and form a type of soldering, they did it to my friends car about 2 years ago and it is still working!I just finished rebuilding my 2008 SE R Spec V engine. As it turned out it was an Altima engine with all kind of parts used before I got the car, what a mess. Anyway, it is running smooth as silk, thanks to some of the fellows here, with all their vast knowledge. I learned an awful lot about Nissans.
Where I am right now I am sure I will revisit the engine in my SE R Spec V. The reason is the spark plug tube seals. These seals on none of the Nissans are replaceable as far as I know. They sure aren't replaceable on the Altima, SE R Spec V or the Pathfinder 3.5 Nissan engine.
I have done some research and found there is a way to replace the seals, how well it will hold up, I don't know. That is why I am asking the fellows here who may have tried this. I do know just silicone on the tube seals will not work for long, as our daughter has been down that road. I wound up replacing her engine because of the tube seals leaked oil and the pre-cat situation took her engine down the drain.
The oil fouling the plugs caused raw gas through the already failing catalytic converters and there she went.
I am having the same problem with the tube oil seals leaking on my 2003 Pathfinder 3.5 engine. I caught it just before it started to foul a plug so I really lucked out there. The catalytic converters are new and I sure don't want to replace them.
When I rebuilt the engine in my SE R Spec V, I didn't replace the valve cover and now I am concerned I may have a leak down the road some time.
I have watched a video where a fellow cut the old tube seals out of the valve cover and used seals from a 2010 Honda Civic that fit perfect in the hole, after the old seal is removed. He used a sealer and said it worked for him. I don't know if this forum will allow a member to post a video or not so I won't until I know for sure. If it is allowed, I will post the video so you can see how he did it.
Has anyone else tried this or have another way to keep from buying the high dollar valve covers. I don't trust the cheaper ones and the high dollar ones are really high dollar something like $200 and up.