I have sent my 1Dx back to Canon twice (CPS free cleanings) and have bought the Copper Hill cleaning kit to do it more often. It's not hard to do yourself. My sensor was getting filthy after every shoot. And I don't change lenses on it in the field. It is most certainly an issue with the lubricant used to keep that shutter moving so fast in the burst modes. To contrast...my 5D mk3 which has about the same number of shutter clicks has yet to need cleaning. I have about 20k on each. Hopefully the oil on the 1Dx will start diminishing as someone earlier mentioned! I love the camera but shooting aircraft is a nightmare in AZ as our skies are mostly blue and show dirt like crazy! Have started using an ND filter to keep apertures lower but I'm seeing dirt even at f8!