Hi,
It will be better if you can upload some images here so we can diagnose your issue (pictures and CMYK at 50-60% coverage).
I just suppose it is about the IBT unit, which can be very contaminated inside.
Gabi
I have a Workcentre 7845. Have been having issues withthe middle of the page not being solid. Most notable on black image only. Have just changed out R1 drum, was showing zero. All other supplies look good. Fresh black ink cartridge has been installed. Not sure about the life of the developer, have had the machine for a few years and have not had any one service machine.
Thank you