Not to get on the Zeiss bashing, but I had a 3-9 Diavari-C that was on my .340 Weatherby for over 20 years, and it seemed to stop holding the zero. I sent it back to Zeiss, and they replaced the tractor spring and returned it to me, no charge. When I looked through it, there were several black specks in the field of view near the crosshair, similar to what the OP has in his Nightforce. I figured that if they screwed that up, what else did they miss. I sold it, and got a Zeiss Conquest 4.5-14, and that never seemed right. Field of view seemed "tunnel vision", and focus wasn't crisp as I expected. I sold that and now have a Swaro 3.5-18 with BRH, and love it. Zeiss seemed to fall a little in the QC, IMHO.
I understand that another company (Minox or something like that) services the Zeiss scopes that are returned now.