That's interesting, I will have to check it out now. Usually oil isn't supposed to be leaking in there anyway but I wouldn't be surprised if Nissan thought it might.
Yes I see what you're saying now. The timing chain indeed does not have a service interval listed and it's supposed to be a lifetime part (which we all know it isn't). I swear, some mechanics will recommend replacing the chain at 200,000 miles as maintenance. It's just a case of conflicting view points at this point. There are tons of TSBs though telling you to replace the guides. http://www.ehow.com/facts_8041291_replace-nissan-frontier-timing-chain.html
I find it weird how they don't list the chain guides as an interval as they SHOULD be considered a maintenance item but aren't. I guess the mileage they are supposed to be replaced at (or at least the manufacturer of the engine hopes so) is too high for anyone to even bother. Maybe at that point you are required to just rebuild the engine anyway?