My D800 had the same issue, oil spots on the sensor (I have a very early copy, and this has been the only issue thru about 4k clicks). The spots were so incredibly tiny it made it very difficult to clean myself….in fact I seemed to be making it worse, so I sent it in to Nikon Service.
The Nikon USA service was absolutely outstanding. Go to the website, fill out the requested service. They give you a UPS account bar code for discounted shipping. They checked and cleaned it, all inside of a week and overnight shipped it back. All of this happened so fast; in fact I got the mail copy to approve the zero cost charge of services the day after the camera came back!