As mentioned earlier, make sure Nissan knows you are serious about establishing why the failure happened, not just a strongly worded letter or phone calls.
Personally i would have parts tested by a metalurgist and gain reports from an independent specialist and also see if you can find other people who have had similar problems, a voice in numbers will always help and seems a few other members have mentioned issues earlier in the thread. Also worth mentioning forums.
On a minor level i had a few problems years ago with Yamaha, it wasnt until i threatened testing of the failing part did they actually play ball.
Good luck and dont give up there imho.
See what happens when the old one comes out