Hello, I am pleased to have the opportunity to assist you. My name is ***** ***** I can help you solve your problem.
I have two HP Office Jet Pro 8600 printers, and they have both developed this problem. The vertical line that you see is caused by a particle of dust that has collected in scanner portion of the Automatic Document Feeder, which paints a line as the paper goes by. Unfortunately, it costs around $160 to have the printer serviced. Even if the source of the problem were eliminated, it would probably occur again. Unless you can do the work yourself, I recommend just living with it, due to both the susceptibility and the cost of repair.
You must have great technique, if you have succeeded in removing the dust particle. What did you use to clean the scanning area and the lens area? Would you care to share your secret?
I have not been able to access the lens area. How do you expose the scanning lens so that you can clean it with a lens cloth?