I have about 6000 shots on my new D600. I moved up from a D7000 and that never had any real spots that I could find. As a newbie to sensor cleaning, I'm looking for an opinion on whether it's worth sending back to Nikon or risk voiding my warrantee by cleaning myself. Is there a way to tell if it's just dust, or is it oil? My concern with sending it back is risking damage in shipment (never mind being without my camera). My concern with cleaning it myself is that I will screw it up. I attached a shot of my sensor. Any help/insights are appreciated.