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Mine spewed out tons of oil over and over again at first, it was shockingly bad, never saw anything like it in the Canon world. Oil everywhere. There'd be dozens of spots on every image. Yes, I'm positive it was oil. It'd show up at f4 and 5.6, some of the larger spots, in any solid color area like sky. Ugly "rings". I usually shoot between f/5.6 and f/13 so it was a massive problem for me.
*insert the: "oh noez! you shouldn't use f/13, you loser, y u get d800 to shoot f/13!" arguments here*.
Anyway I wet cleaned it. Had to do this many times. After probably about 1,000-2,000 shots or so it is just fine, doesn't have issues. Might get some dust specks sometimes but dust is no biggie, blows right off who cares. Now that the oil is gone it's no worse than my canon 7d, 60d, rebel xsi, my gf's 5d3, etc.
If that poor QC was the price I had to pay to get this awesome camera for $3,000...meh, I'll take it! Wet cleaning is quick 'n easy. However, that is just my point of view. Others may think "for $3,000 I should NOT be cleaning oil off the sensor". And that point of view is totally valid.
My only real complaint is Nikon's lack of communication regarding the issue. Canon had an issue like this with oil and they apologized and communicated.
Edit: The oil issue will show up regardless of whether or not you change lenses out in the field. I change lenses out hiking all the time (in windy dirty pacific northwest) and have no problems now that the oil stuff is gone. The even bigger issue with oil is that it also prevents the blower from blowing dust particles and such off the sensor. The oil sticks 'em on their like glue!