The drum unit (seperate from toner on Brother lasers) is wearing out. After replacing it — or to clear a premature warning — you must reset the drum counter.
Work through these in order; most people are fixed by the first two or three.
Slide the green corona-wire tab back and forth a few times to clear streaks before deciding to replace.
After fitting a new drum, reset the counter (commonly: open the front cover, press the panel sequence for your model, confirm the drum reset).
If prints show repeating defects and cleaning/reset don't help, install a new drum unit.
Poor-quality drums/toner shorten drum life and cause marks.
Browse step-by-step setup guides, error-code fixes and driver help for every major brand sold across the USA & Canada.