Black line down side of scanned page only when double sided

[GabiE-Xerox]

Hi,

Could be a bad contact at the flat cable of the DADF CIS (scanner) at the CIS or at the ESS board or even a defective DADF CIS (unfortunetly the CIS cannot be replaced separately, you must replace the hole DADF).

Gabi

[mjbarnard1]

Versalink C405DN

Has recently developed an issue with scanning (or copying). A 2cm black line appears along the entire left side of the page - but only on the second page when double sided scanning from the ADF. The first page is always fine, as is the flatbed scanner. There are no problems printing - this is a second side duplex scanning issue only. 

I have cleaned everything I can find - including https://www.support.xerox.com/en-us/article/en/x_vlc400_en-O2797 but clearly there is a part of the scanning which scans the reverse side that I have not been able to locate. 

Any ideas?