Dust on drum - Brother MFC-8460N All-In-One Printer

There is a blue colored slider on the drum unit, move it side-to-side 10 times.

Open the front of the machine.The drum is part of the toner cartridge.

Turn the cartridge upside down. Look at the long cylinder, it should have NO toner dust on it. If it does, the cartridge is bad and must be replaced.

On most fax machines a Dust on Drum error simply means that the drum unit needs to be removed and the charger cleaned by sliding the small built in charger cleaner back and forth but be sure to place it back in it's home position or your received faxes and copies will have a blank line thru them. See your operators guide for more details.

take the drum out and clean the grid on the drum unit. this is called the corona wire in the grid

The dust on the drum message will persist if the corona wire cannot be cleaned by sliding the blue tab repeatedly left to right. You'll need to replace the drum unit.

"Drum error" is because there is dust or any thing like ink on the drum.
After I filled the toner with a other brand dry ink, I got this message.
I carefully checked the drum, I found there was some ink on the drum. So took off the toner part, washed the drum kit with the tap water. wait it dry. There is a rubber roller inside, it will take time to dry.
after the drum kit dry, I rolled the drum, there still something on the drum, I use a tissue paper cleared it.
put the toner back, insert it back to the printer. It is fixed.

If the drum has marks on it, you might have to replace it.  Sometimes the fuser rollers can leave marks on them as well.
Check for lines on the drum first.  If they are there, it could need a drum replacement.

Dust on drum is an issue with the corona wire. Use the blue tab on top of the drum unit. Slide it back and forth 10+ times and this should correct your issue.

Good luck!

try using canned air to clean the coruna chagre wire assy

Dust on drum refers to as you correctly stated the wire, it carries a electric charge that transfers the image. If the wire gets contaminated the electricity dont flow right so dust on drum is desplayed, you drum cart is faulty, they are not repairable items, go buy another then claim new/old one as faulty from them. Um aH.