I have same problem on my C309-g. Have done all you described as well as uninstalling printer, removing (using Revo Uninstallerr) all HP related software, hardware and reinstalling as a new system. Same results. I suspect a hardware problem. FWIW I have had this printer 3 1/2 yr. and produced 4100 copies problem-free. Only odd thing is that I successfully printed 135 pg iPad manual the evening before without a hitch (using 2-sided printing). Now this happens the next AM and I get magenta or pale green print (faded); no black.
I have no clue as to what to try next.