Xerox 242 Leaving a Mark

My Docucolor 242 is leaving a mark in the same general area but not on every page. Out of 100 sheets I get about 30 with it on it. I took out the cleaning assembly and cleaned it. All the drums are new. The mark is usually magenta or yellow. Any ideas what this could be?

 

How you changed or examined the drums after you discovered the marks?
What do the marks look like? Tiny specs or dots? Little crows feet? dashes?
You're running 8.5x11 sheets?

 

I'm running 11x17. I'm wondering if the IBT belt has an issue. I rotated the image and the marks are different.

 

Definitely looks like residual toner is building up someplace in the machine and depositing back onto the prints. specs would have been a nick in the drum or developer leaking. The crows feet would have been a transfer or electrical problem.

You say it varies in color? its not just one imaging unit? And you say you looked at the machines cleaning elements? Looks like a problem with a cleaner...