I would call them and talk to them but what they told me is that they would evaluate it and either clean the sensor or replace the shutter. My brother bought a used D600, it developed the problem, Nikon replaced the shutter. Mine is going in Friday. But you would be smart to have your own discussion with Nikon.
Chris T wrote:
Do you mean, RC ... one can go ahead and buy a D600 used, and then, immediately, turn around and send it to Nikon for a free shutter replacement?