I have a C400 were the print is not that dark.The magenta is faded and the patch placed on the transfer belt is not that dense .It has all new image units and I have replace the high and low voltage power supplies, MCU ,transfer belt and secondary transfer roller.I have removed and cleaned the laser assembly and done a NVMRAM INIT and tried to adjust the Transfer roller bias.The software has been upgraded and toner is getting to the image units.I suppose the next step is to try the ESS or new laser assembly.Any thoughts?It is a machine we got used from a wholesaler so my thoughts are its not worth being fixed.