If I print a solid page of magenta: perfect. Solid page of yellow: perfect. Solid page of blue: perfect.
But a solid page of black: extremely faded, and blotches all over the margins.
I once tried a non-Xerox cartridge, but since then I've tried several genuine Xerox black cartridges (all the color cartridges are genuine as well). Still no improvement.
Thanks for the idea, but as mentioned I've tried several genuine Xerox black toner cartridges, and the problem persists. Clearly not a cartridge problem.