We have a Brothers printer HL-5350 DN at our housing project. Its a really greate device, I have to say at first.
But it has one bad habit: the toner cartridge is reported as empty more hurried then it's necessary. Knowing this, I researched a little at the internet one year ago. I found a nice hacky workaround, that let me able to print the toner cartridge till it is really empty.
The hack, let me call it level 1 hack, works like this:

Level 1:
Open the printer and take out the toner with drum, then take the toner out of the drum too. There you can see a round hole. Just use some black sticky tape or some other colour and paint it black to cover the "window". That's all. Now your printer see a full toner and prints perfect results like it did the last print before stopping its work.

After this hack, we printed maybe 1000 pages more (really one thousend) then the printing results getting unusable.

I went to a refill service and got back a full loaded toner cartridge (you can see the - maybe - hot glue closed aperture on the picture).

We use the refilled toner with satisfaction.
But on page 7xxxx the printer led said, that the toner cartridge will be empty soon. I just did level 1 hack again (was removed at this time) but it doesn't help.

Then researched again and found a very nice, but very long thread about this printer toners.

After reading a while, I knew what to do: its time for a level 2 hack :)

Level 2:
Take out the toner like in level 1. Remove the screws on the side of the gears. Remove the black cover and search the gear with a clip, it is called "flag gear". It engages after a fix turns of the toner rolle. Remove the gear and put the clip to the default position. Put the gear back on the clip. Be carefull and turn the gear to the position, you can see on the picture below.

Thats it. Now you can print as long as toner powder exists. In my case, as long as the results of printing are usable ;)
After this among time of dirty hacks, maybe we will buy a new one after the next refill.

Feel free to reproduce this instruction.

But I dont warrent, if the printer damages, steel your wife or kills the naughtborhoods cat. Allways be carefull with dirty hacks...