Sorry to bring back this old horse to life just to beat it a little more.

Today a colleague of mine told me this absolute gem of a conversation (not exact words, but the meaning is there):

ThisColleague: "So, what is the problem you can't figure out [on a color midrange Ricoh machine]?"
OtherColleague: "Well, it's a line that repeats on all colours. I replaced the belt cleaning unit, but the problem is still there!"
TC: "Okay, what color is the line?"
OC: "It's black!"
TC: "And you still didn't figure out where the problem comes from?"
OC: "No, it happens in all colors!"
TC: "Dude, it's a BLACK line, did you check the black IU?"
OC: "Why, is the black drum always in contact with the belt?"

Insert facepalm here.

TC is a forum dweller, he might want to chime in to give some more details, but this surely made my day!