There are a some debris inside black developer housing and the IBT assembly is very dirty inside. So you need to replace the black developer material and the IBT assy.
I am in the military and am a “Technician” of the equipment with minimal training. My publications do not address the issue I am seeing. The issue I am having with my machine is similar to outboard deletion in all colors but it is only on the top 1/4 of the page when printing solid colors. When printing text it is only faded at the point that the solid color would be faded but when printing multiple pages it is noticeable. When I printed different diagnostics, the grids came out with good quality, no fading. I have posted pictures below.