Every page that prints on my Canon MP830 now has a 1/4" black vertical stripe on the BACK, 3 1/2" from the left edge. The nozzle check prints a perfect pattern in all colors including both blacks but does have the black stripe on the back. I have tried cleaning, deep cleaning, roller cleaning and bottom plate cleaning as well as removing the ink cartridges and the printhead and cleaning the printhead and the printer very thoroughly. As soon as I reassemble and print 1 sheet the stripe is back. I contacted Canon customer support and they suggested taking it in to an authorized repair station and offered to let me buy a different new printer at a discounted price under their CustomerLoyalty program. I use only genuine Canon cartridges abd currently have 49 in stock (I print a lot) so replacing the printer is not a cost effective option. I and have replaced the Black 5 (large black) and the Black 8 (small black) numerous times but nothing seems to help. I was wondering if the printhead has failed and now allows one of the Black cartridges to leak onto the bottom plate, etc. There seems to be a lot of black ink on the metal roller where the paper is delivered from the printer into the tray. It comes back right after I clean it. Please advise.