The owner of this 5d has dropped one day his camera from a few centimeters. After that, the AF-feedback lights disappeared from the viewfinder.
I disassembled the body, and I have found the broken small LED board, which emits his light precisely on the place where the marks are engraved on the small plastic window above the matte. There is a very delicate small optical system there, some mirrors and lenses.
The last picture is the glued board (in the last time I use on expensive, but very-very good 2 komponent glue, the loctite 3090. it’s extremely rapid, very strong, and after solidifying is transparent.)
After assembling the camera again, I observed the deep marks on the top of the body. (don’t ask me, why not before. At midnight sometimes I am not always working logically)
Next day I told to the guy, that perhaps it was a big flight of the camera.
But no. He was only the second owner. The deep fingerprints on the housing were made before. The feedback board was probably broken for a long time, but stucked at that place. The next (smaller) shock was necessary to get it out from there.
The autofocus was affected too….