I have purchased 4 new developer housing units and will update when I replace them. I decided to just replace them all, as I think the cyan is on its last leg too as im getting blue splotches here and there. So I will update when I have them replaced just for future users with a similar problem!
Magenta and Yellow make Red so the problem is in Magenta. Its either the Magents developer housing, the Magents 1st btr in the ibt or the ROS window. Clean the Magenta ROS window with the cleaning wand.
It can't really be a drum and go all the way across the page in all colors, and Coke red has CMYK: 0, 0.881, 0.907, 0.070 values (approx) so it certainly won't drop cyan on it. Yet Cyan is on all the streaks.
Since you replaced the belt, its cleaner, the fuser, the only thing left really is a leaking developer.
Assuming it happens on copies as well as the prints
I have a workcentre 7345, and every time I print something, I get some faded lines with some blue splotches scattered throughout, across every page that prints. It is always in the same spot and it covers the entire page from left to right.
I have attached some pictures for reference.
Things done: replaced all four drums, replaced the IBT transfer belt/cleaner (the whole assembly), replaced the fuser, and cleaned inside as thoroughly as I could. The issue still persists.
It is always in color. It is not noticeable when printing in black and white, and it seems to go across all colors, not just one particular color (however the lines are always yellow with the blue spots).