I am about to send my D600 back for the 2nd time in 6 months. The camera had the shutter mechanism replaced but the spots are back and worse than before. I think when I get it back this time I will sell it on Ebay and switch to either Sony or Canon. I know all DSLR's have some dust issues but this is unacceptable. The sensor should not need to be factory cleaned every 2 months. Nikon either will not tell us what is really causing the issue or they just have no clue even after all this time. I have lost my faith in Nikon after 40 years. Shame on them.