Put your D800 on a tripod, throw your fastest lens on it, aperture priority wide open, select the left-most AF sensor and point that sensor at something with some detail you can focus on. Set the camera to AF and let it take the picture. Then switch to manual focus without moving the camera, turn on live view and magnify in on that same spot as far as you can go and then focus it by hand. If you have a magnifier you can use on the live view LCD while you manually focus that will assist with getting critical MF. Take the picture. Then on your computer zoom in to that spot on each shot and see if the autofocus shot is more out of focus than the manual focus shot. If it has the left side focus issue it will probably be quite a bit more out of focus ( as mine was ).