I'm including the link below that works and includes instructions. Please review and follow these steps:
https://support.brother.com/g/b/faqend.aspx?c=us&lang=en&prod=ads2800w_all&faqid=faq00000261_059

Instructions:
A spot of dirt or correction fluid on the glass strip may cause poor-quality scans. Clean the inside of the scanner if a vertical line appears in the scanned data or if areas are missing in the scanned data.
 
Follow the steps below to clean the inside of the scanner.

NOTE: Illustrations shown below are from a representative product and may differ from your Brother machine.
 
  1. Unplug the machine from the AC power outlet (electrical socket).
  2. Remove the Automatic Document Feeder (ADF) (1) while releasing the levers on the back side.
    Remove the ADF
  3. Open the Front Cover (1).
    Open the Front Cover
  4. From the back of the machine, in the ADF unit clean the glass strips (1) (2) with a soft, lint-free cloth moistened with water.
    Clean the glass strips
  5. Pinch both sides of the Reverse Roller Cover (1) and pull the Cover down.
    Pull the Reverse Roller Cover down
  6. To remove the Reverse Roller, grab its shaft and pull it toward you and out to the right.
    Pull the Reverse Roller out of the machine
  7. Clean the Reverse Roller with a soft, lint-free cloth slightly moistened with water.
  8. Slide the Reverse Roller (1) into the left opening to place it back into the machine.
    Place the Reverse Roller into the machine
  9. Close the Reverse Roller Cover.
  10. Clean the Pick Up Roller from side to side with a soft lint-free cloth slightly moistened with water.
    Clean the Pick Up Roller
  11. Close the Front Cover and attach the ADF.
  12. Plug the power cord back into the AC power outlet (electrical socket).
  13. Do one of the following:

    (For the models with machine's display (hereinafter called LCD))
    When the LCD instructs you to reset the counter, follow the instructions on the display.

    (For the models without LCD)
    1. Open the Front Cover.
    2. Press Assign3 for about five seconds until the machine beeps to reset the Periodic Cleaning Counter.

Thank you,