Have you ever had an electronic item say a TV which sometimes work sometimes dont but you cannot pinpoint the problem? Send to repair shop also cannot solve? You found out later, that it was fixed with an inferior component.

Or when you buy a car, start wonderfully every morning, but after a month, cannot start because there is a problem with the alternator. After inspection, you found out that the alternator was a rebuilt alternator which is waiting for its death.

I'm just stating the logic from experience. Things can happen. Let's wait for nikon center report and testimony from seller's friend.