I called Canon yesterday and they told me they would take my MK3 into the Irvine CA Service Center and apply the "Light Leak Counter Measures" on my body and they sent me a pre-paid UPS label.
I think I'll get my 50mm F/1.2 mirror adjusted at the same time.
They have my camera in a pile waiting to sell as a refurb in 6 months or so. I bought a 1D MK IV to replace it for about the same price. I also bought a D800 to try out and see for myself how it compares. So far, the only thing I do not like about it is the eyepiece and the huge files. When I've underexposed, I can pull up a image in the shadows way beyond what I could do with my 5D MK III. I have been saving jpegs to the SD card, so after 1000 images, I took a look at them and compared them with my processed raws. The raws are better, but the 12mp jpegs are suprisingly good. There is so much detail that a lot is retained even after in camera processing.
If only Nikon had a 135mm L, and a 100mmL with the super IS. I'm reluctant to replace my Canon lenses with Nikon, but it does hold its value.
There is a mirror in a 50mm f/1.2?