Check your camera to see if it needs a slight lube job
If you're currently shooting with one of Canon's top dog cameras, there's a service advisory out today that you should be aware of. According to the Canon site, there has been an issue reported where insufficient lubrication in the 1D X or 1D C causes the internal driving mechanisms to wear prematurely. As a result, this can affect the camera's ability to achieve focus.
Here's how to tell if you have an affected model:
Potentially Affected Products
1. EOS-1D X: If the sixth digit of the serial number is “1”, “2”, “3”, “4”, “5”, “6” or “7”, the phenomena described above may occur.
2. EOS-1D C: If the sixth digit of the serial number is “1”, the phenomena described above may occur.
The markings shown in the cameras above mean that they're unaffected by the issue.
Service needs to be done at a service center and will obviously be free. And, since most shooters using at camera at this level likely have Canon Professional Services accounts, expedited service should be available.