First of all replace the toner cartridge, if it doesn't clear, check the developer unit for any gear wornout and rectify. This should solve your problem, good luck!
dont know if there is one. https://www.scribd.com/doc/98960686/Panasonic-DP-8020e-Service-Handbook ftp://ftp.panasonic.com/printer/om/dp-8020e_driver_en_om.pdf but those links may help you in other ways.