Is it normal to see black powder on my toner cartridge & drum for my Brother HL-2170w laser printer?

I opened my printer to change the drum unit and I noticed a lot of black powder on top of the toner and the drum unit.

• Is this normal?
• Does this mean the drum unit/toner is bad?
• Should I just change both of them or can I just change one?
• If I change one, say just the toner, but the drum unit is bad - will it damage the new toner cartridge - and vice versa?

I cleaned the dust powder (which I guess is toner) off, but the printer still prints dirty.

Thanks.

Edit 1: All of this stems from this question - Can a generic drum unit cause a Brother HL-2170w Laser B&W printer print dirty?

Toner dust is gonna happen, so don't worry too much.

However, if you start getting unfused toner on your output paper, it could be a sign of a bad fuser roller and you may need to replace it.