Just wanted to share a problem I had with my new Brother 7820N printer. On the underside of its lid, against the left edge, there is are two small, white rollers. It helps documents from the ADF pass through correctly. Without the rollers, documents jam. This prevents multi-sheet copy/scan functionality.
Recently, this device became loose when a small spring device fell off. The spring itself has a loop on it, which is situated around a small plastic protrusion. This protrusion broke off somehow, thus allowing the spring to fall free, which allowed the white rollers to come off as well.
Super-gluing the plastic protrusion back did not work - the spring exerts too much pressure for the glue to hold it. I instead was able to take a thin piece of plastic and glue it over the same place as a part of the spring, which acted to hold in the metal bar that secures the rollers.
Now all is well again with the Brother printer and the functionality of a working ADF.