Lens of D800 AF issue

... All things equal, using the view finder, the right and left should be the same.  In other words, equally out of focus or unable to lock on the target.  If the right can lock and focus, even if not as well as the center, but the left locks and is noticeably worse then than the right, you may have the D800 left bank defect.

The key is that all things in the test must be equal: wide fast lens wide open, same exact target and lighting, tripod, etc.