We are having an issue where our 6280DN is using a lot of Black toner. We just installed a brand new black cartrige and fuser less that a week ago. We've had the printer 5+ yrs without this issue. I've set the driver to economy for all users.
What could cause this besides page counts/printing?
If it isn't on the paper coming out then it is dumping it inside the machine (can't vanish)
You would need to verify that people are not printing more and take apart the machine to find out if something is broken and toner is dumping into the printer.