I have seen spots that look like this. Some were easily removed with the rocket blower. I find that making sure the camera is sensor is pointing down during an air cleaning and the blower nozzle is used at various angles helps.
Some of the spots I had needed a single pass with a wet swab from Visible Dust to be removed. I think what I had was dust because they were removed easily. Dust isn't a deal breaking issue for me because I know I'm going to get dust on the sensor with regular use.
If you are uncomfortable with cleaning your own sensor filter you might want to exchange the camera. I have heard reports of dirty sensors on D800 and other cameras as well.
I know there have been several reputable reports of dust on D600 sensors but I haven't seen any *confirmed* reports of oil.