Heh. I might have relevant experience.
I started out using w/e was the cheap Brother printer 10 years ago, but it only worked with generic refill cartridges. And those generic refill cartridges quickly degraded (the drum?) - blacks started to become washed out and streaks and other artifacts would appear all over. From what I can tell, the genuine Brother toner for this specific printer (350N is the model of the refill, IIRC) had a higher melting point. I'm guessing the fuser in this model is too hot for the generic refills, despite what the sellers claim.
Now I use HP 1102W. I have only ever used the genuine cartridges for this printer. It works fine for me down to 8 mil traces. 6 mil is where fine breaks start to occur.
FWIW, in Eagle, it is important to check the box next to "black" in the print menu, else it will print some of the layers with fine stripes and/or shades of grey. Specifically, the top and bottom copper layers come out fine, but pads would grey out and degrade in the etch. It was several boards before I noticed the cause of this subtle problem.