Mine was brilliant and now it's sad and none of the troubleshooting steps for the symptoms I'm getting actually work. I suspect the room it's in is too cold and humid and that's making the toner clump, but I'm not keen on replacing mostly-full cartridges as the price has more than doubled since I got the printer.
Try putting the cartridges in a dehumidifier or wrapping them in paper and placing them on top of your radiators for a few hours, just be careful that they don't get too hot (more than 50°C could be problematic)