WC 7328 .. the Copies is getting lighter and lighter in the bottom of the section only and it only happens in BLACK. Other colors are fine. After making 10 copies, cant really see it anymore. after shut it off and wait for a day, turn it back on. I can make another 10 copies again but cant really see after that. Again, only happen on the bottom section of the page. I changed the toner and drum cartridge already. Anyone knows what is wrong? thank you.