Vertical line on scans when using doc feeder

[Upeva]

I get a vertical line on scans when using the document feeder but not the flatbed. I have cleaned the document feeder glass as suggested to others who have had this but the problem persists. I understand that on this model there is a potential hardware solution by replacing a part (that I don't know of) so I'm posting here to see if anyone knows of a hardware fix for the vertical line on document feeder scans when cleaning the machine (multiple times) did not solve the problem. The machine is out of warranty and I'd like to try to fix it rather than trash it.

[Repairatrooper]

The 477 can be tricky because of a small mylar strip that HP users over the slit glass for the ADF. Foreign material can get under the mylar and be near impossible to clean. Keep in mind that even the tiniest spec of material such as adhesive from a post it note can be impossible to see but will refract light and cause scan defects. One way to make sure that it is not something on the glass is to scan a piece of white paper and then set the resulting copy against the glass so you can see exatly where the defects may be on the glass.

[Upeva]

Yes, I've scanned a blank sheet of white paper and cleaned accordingly with no change to the black line. FYI the line I get is about 1/16" wide and there is nothing visible on the slit glass after multiple cleanings, not a smudge or smear, even under a magnifying glass that could cause the line. Any other ideas or thoughts?