My printer is saying my drum unit is empty. is that just the laser ink cartridge or something else?

I'm not sure of the design and implementation on Brother units but on most designs that I am aware of, the answer is yes. The imaging drum is contained within the print cartridge.

Normally I would expect that you run out of toner long before the end of life on the drum. Sometimes people get after market or refilled cartridges to save on cost and open themselves up to situations like this.

When printer manufacturer's offer refurbished print cartridges, they are offering an "ETN" (Equivalent to new) cartridges. That means that the cartridge has be completley rebuilt. This would include replacing the drum

Third party and cartridge re fillers do not do this.

So now you are faced with either taking the print cartridge apart and replacing the drum or purchasing a new print cartridge.

I would get a factory new Brother cartridge and not waste my time on refilled or third party cartridges. They are not worth the money and have been know to cause print quality problems and void warranties on printers.

Don