I have a customer who has put over 10 yellow drums in a 7400dn.
Down the center of the page about 4 inches wide there is a yellow haze in the background on both sides of the paper after they duplex.
They have put in a transfer belt and a waste toner auger assy. Also I swapped the yellow drum for the magenta,cyan and black , no matter where I put the yellow drum it always put in this yellow back ground. I can see a yellow haze on the drum when I pull back the flap and there is a yellow haze on the transfer belt starting where ever the yellow drum is at the time. They had a used yellow drum that said it was at the end of life, I put that in ad it printed beautiful with no back ground. Now it's failing due to the drum being at end of life.