I'm curious. I have the exact same Magenta cartridge problem too. Buy new one, no difference - almost no color at all.
I see this thread goes back several years, and yet I haven't seen one single reply from an HP Technician. Does this mean they don't monitor the forums at all? Or does it mean the don't have an answer and are too scared ot post? I just find it odd that they haven't bothered to make a single suggestion in what appears to be over 4 years....