Workcentre 7830 random toner smudge

[Codex]

Hello

i,'m going mad with a WC 7830, the machine makes random black toner smudges (looks like short stripes) on the machine side.I changed black, yellow and magenta drums (end of life), transfer cleaning unit, Cyan Development unit ( defect on the mag roller), but the problem still occurs randomly, it's a problem because the customer needs absolute clean prints.

ANY IDEAS???? PLEASE HELP!!!!

[CopierTechofOmens]

Re: Workcentre 7830 random toner smudge

Attach a sample of the defect

[Codex]

Re: Workcentre 7830 random toner smudge

Made a lot of tests yesterday, turned out to be the black developer inside the unit, because of the heat or because the customer leaves the machine unused for many time, the developer was hardened inside the unit.