A black line is printing on the left side of the

If it is only when copying, the problem is with the scanner, but if you are printing from computer and it still does that, you most likely need to replace the drum unit. Even though you can reset drum many times, they do go bad after a few resets. eBay has them at a very low cost. I'll share a link bnelow of an example: TN650 Toner DR620 Drum Combo for Brother MFC 8480DN HL 5370DW MFC 8690DW...

If you are seeing vertical streaks/black lines your primary corona wire is dirty and or the fax scanner may be dirty.
1)To clean the corona wire you take the drum unit and toner cartridge and place it on disposable paper to avoid spilling.
2) Clean the primary corona wire inside the drum unit by sliding the blue tab from right to left several times.
3) Return the blue tab and snap it into the home position.
4) Reinstall the drum unit and toner cartridge.
5) Close the front cover.
Caution: if you do not return the blue tab to the home position it may repeat the black lines.

I forget the terminology but I believe there's either dirt or a sheet of paper on an internal roller.

You might try here for HP help.

Usually this is occurs when the drum needs to be changed.

Try running its Clean Cartridges command.

...maybe its time to replace fuser fixing film!?

this is a catridge problem so pls replace your printer catridge.

inside the printer on the paper pulling roller there will be some powder got collected on it due to this a black line appears on the paper.the power faLLS FROM THE TONER WHEN THE WASTE POWDER COLLECTING SECTION IN THE TONER GETS FULL SO IT FALLS on the roller while printing and this happens.take a air blower .bolw in to all the parts of the printer.keep the printer off .remove the toner cartridge.and keep the toner assessing door opened.and then blow the air in the printer.and then check out.

Change the toner cartridge, refilling will not solve the problem.

On the ADF check the twink mark on glass scanning mirror