When remove the imaging units (drums), under them must be the developer housings (that ones with some rollers with CMYK toner on them). But maybe is better to replace the imaging units if you said they are nearly to replace.
Our Phaser 7100 has started printing black marks on pages quite randomly.
We've recently changed the black imaging unit and toner and have run several pages through the printer. Everything is fine for a while then we get a pages with black marks and streaks.
We need to replace the C, M & Y imaging units soon.
We've cleaned everything we can find instructions for - we'd appreciate some ideas about how to fix this.