Canon 8800F - line in scans

[02Pilot]

My Canon 8800F is producing a thin, slightly dark line consistently in the same place in all scans. I know that this sort of problem is often caused by dirt or debris in the calibration area, but that is not the case here; I have cleaned the whole glass surface and the light source screen thoroughly and inspected with a bright LED. I have the scanner set to calibrate before each scan, so it's not the legacy of dirt in that area either. I'm fearing it may be something internal, but I'm not sure how to confirm this, let alone rectify it. Any thoughts or suggestions would be appreciated.

 

[02Pilot]

Problem solved. Under an even brighter LED light I saw that the inside surface of the glass was slightly fogged, with a single line clean (presumably where some part of the carriage touches it). I disassembled the scanner, cleaned both surfaces of the glass, and reassembled. The line is now gone.