I can't seem to locate the site at this time, but about two months ago, I visited a web site that reviewed the D600 with regard to a "repairability review". This was at the height of the "oil on sensor" issue which is "said to be" no longer an issue. I wonder how that is going to be affected by the existence of pre-fix cameras in the distribution pipeline.
Some sort of serial number cutoff, I would suspect. At least it appears that Nikon finally quit "stonewalling" buyers and admitted the problem.
Back to the repairability, I will take another crack at locating the site.
Two things I do recall are a very low repairabilit score related to a huge number of small screws internally, and the fact that none of the internal screws are secured into brass bosses in the body. All assembly screws are screwed directly into the plastic of the body. That's what I recall, and I will post the site if I find it.
Found... scores 2 out of 10 on repairability. See the link;
http://www.dpreview.com/news/2012/11/08/ifixit-tears-down-nikon-d600-chipworks
There are other simila finds on the internet... search the words:
D600 repairability