I get vertical lines running down the middle of paper

When you use the flatbed the copy is perfect because the ccd sensor is under the glass cover and obviously is free form dust/ dirt.
On the other hand if you use the feeder the ccd sensor is located in between the roller assembly (not sure exactly for this model).
This means that the page is scanned by the ccd in the feeder, any dirt on the ccd will appear as a black line. I assume that you are feeding papers from the side and not from the top that is why you get a horizontal line.

A quick test to see if the ccd sensor is dirty is to feed the paper from the top side to the feeder. If you get a vertical line it is a proof that your ccd sensor needs to be cleaned.
The worst case is that the sensor in the feeder assembly has a tiny spot that is damaged and it is causing the black line.
So , first try the test, then open the feeder assembly, locate the ccd and clean it. Hope that this helps.

Check your flat bed and Document feeder scanning glass need to be clean, if any dot or dust in scanning glass of document feeder it will appear a line, check this points first
1- Check printouts from computer or FAX if it is clean problem in scanning section
2- Check using Copying a blank paper using only Flatbed if it prints without any line its problem from document feeder Scanning glass
So solution is clean the Document feeder scanning glass using wet cloth, note careful about wet cloth switch off the machine and clean it

Open adf unit, spray little quantity if ISO alcohol clean with smooth cloth especially small glass. ensure that when you are using ADF avoid wet whitener/glues on paper.

This black line sounds like it is definately coming from the ADF scanner glass. This is the thinner strip of glass that is located just to the left of the large original glass. You can verify this by making a copy from the large glass instead of using the feeder on top. If the copy comes out clean then it is definately the scanner glass. Just clean the glass well with glass cleaner and a soft cloth. This glass is only used when copying/scanning using the top automatic feeder
Good Luck and Thank You for using Fixya.
WheatlandServices

Get a paper towel and a little glass cleaner and clean all the glass under the doc feeder. The line comes from the scanner seeing a spot as the paper is passed by it.

For the line problem, open the doc feeder on top and clean the scanner glass.

For the number key problem. drip a small amount of WD-40 down into the sticking key.

You need to clean the glass. Open up the feeder and you have a large piece of glass for scanning and to the left a smaller piece of glass that it uses to scan from the feeder. Clean this smaller piece of glass; even the slightest smudge can leave a black streak.

Open the document feeder and clean the scanner glass.

If the lines are vertical (in the direction the ADF feeds, 11in long for 8 1/2 by 11) You can try cleaning the glass the scanner uses when it's using the document feeder. Pull up the top left part of the printer where the documents feed, there's a little rib in the middle of the side to help you do this, then simply pull up the assembly underneath with all the rollers in it, you should see about an inch of glass underneath and a centimeter long strip of white plastic on the assembly (this serves as the white background when feeding slimmer papers) Clean them both. I'd recomend any glass cleaner, just don't spray it in there, spray it onto a cloth.

lift feeder and look at the thin strip of glass, there will be a dot or something on it. Clean, as the paper is moving the dot looks loike a line to it,