Ran into a couple of these and they are quite nasty to dismantle. First one was solved by replacing the whole ADF ( bought from AliExpress, not quite cheap). But then I found the cause ( one of the motors inside the ADF- the one that drives the pick roller) had a cracked drive gear. The motor is available for purchase ( not where one would expect...
) and the part# is COM39-60006.
There is also a clip on Youtube that helps with installation: https://www.youtube.com/watch?v=v4RH07yo5rw
Good luck !

There is also a clip on Youtube that helps with installation: https://www.youtube.com/watch?v=v4RH07yo5rw
Good luck !