I have been following the issue for some time. My 1DX is only 1 month old and has a number 8 in the serial number's 6th position so this supposedly means that it is manufactured with the "fix" already in place. My understanding of the "fix" for cameras that aren't showing any AF problems is just extra lubrication to prevent the black plastic particles from wearing off and spreading themselves throughout the camera internals. Cameras with actual AF problems are getting the whole mirror box replaced I think.
Now, I personally have not had any AF problems. However, within a few hundred shots I started seeing the small black spots in the viewfinder. They first appeared in the upper right and now I have them in all 4 corners but not many or any in the centre of the frame. I also was getting a lot of oil on the sensor that required a wet swab cleaning as my first attempt with a dry brush just smeared the oil across the sensor. The wet clean worked well.
I am worried. The most detailed information about this problems is in these two DPreview threads. The one poster "tvstaff" is very adamant that there is still a big problem even with serial numbers past the recall (i.e. #8s as no #9s have been reported in the wild yet).
Canon Canada has told the one poster on DPReview that the specs in the prism area (these are the black dots seen through the VF) are not part of the recall problem and don't affect the actual picture (which is true, they are just ugly to look at and disappointing on a $7000 camera). They said they could replace the prism but that would be not covered under warranty or under the recall.
I haven't contacted Canon yet but I'm keeping a close eye on the problem. What we don't know if is the oil just from the excess lubricant to fix the original problem or are these black spots actual physical particles that is wearing off and eventually will affect the AF sensor from working as some have experienced.
Hi, I've also posted about this issue in the above DPReview threads.
I also just bought a 1DX with the "8" in the sixth position (from B&H in September). Within the first 50 shots, I noticed a couple dark black spots in the upper right corner of the viewfinder. Autofocus worked fine. I sent it in for service to Virginia, spots were removed, and I also now have the black mark in the battery compartment. I've been using it now since then, it seems to be working fine. I have noticed a couple spots, which are much smaller than before in the middle top border of the viewfinder, but these are not as obvious as the previous spots.