While I was at work this morning I decided to read my warranty book again. It clearly states in Nissan's own writing something is not covered if it is directly resulting from misuse, alteration, non-approved parts, etc. So they admit in the warranty book that it must be proven that the action or part in question caused the problem for the problem not to be covered. Of course the actual cooler or what ever other part won't be covered unless it is Nissan approved.
With that said this is the reason I always keep my stock parts. If a serious warranty issue occurs I can always put the factory parts back on the affected area or remove the questionable part before taking it in.
I do agree with 6MT in the fact that until someone actually has a serious problem resulting from the high oil temps., there really isn't any legal ground to stand on with this issue. While I'm not a civil lawyer, I have spent plenty of hours in court as a police officer dealing with the legal system and the principle is the same. A precedent must be set before it can be challenged. If someone actually has oil temp related damage and Nissan drags their heels on it then we have something to go on.
Either way we shouldn't have to deal with this issue in the first place. Nissan should quit being a
and retro fit every 370z with an oil cooler.