So my dad brings their 1dsmk3 studio camera home because it wasn't responding to the computer as they only shoot tethered. They never take the lens off the body and every night it's removed from the tripod, unplugged and put into the company safe. I figured I would check all the contact surfaces and blow/clean them. Taking the lens off and examining the pins I noticed lots of staining to the rear lens element. I wonder if this is typical of a camera that never has the lens separated in years. Have to admit, the sensor itself was spotless. The staining appears permanent.
Cleaning the contacts on the usb fixed the non responsive camera, so it wasn't all bad.