The Phaser 6115MFP Knowledge Base has an article (with color pictures) explaining how to clean the laser lens on the machine. Follow the link above and in the search field type, "clean lens" and hit search. The first search result is the article that you are looking for so click on that. It should be titled, "How To Clean the Laser Lens." Follow the instructions and you should be on your way to clean prints.
after 3 years of great service, the printer complained about needing more toner. I replaced all 4 colors with BRAND new Xerox toner and since then I have vertical lines in all my printouts. I put the old toner back in and same thing. The lines go through all the colors when I print a color test paged.
Xerox diagnostic pages says to replace the main charging grid but I cannot find that part anywhere. Any ideas?