make a light color grid and lay it corner-ways on the glass.. make a copy. lay it to the side. make another copy and turn the copier off mid-cycle carefully pull the drum out and check the copy on the drum. check for any bad spots. smears. or skipping. if the drum look good, make another copy turn off when paper starts to emerge inspect paper for copy integrity before the fuser unit generally fuser unit burns and presses image on or into the paper if image is good going in but bad comming out problem is there. fuser has 2 rollers one for heat, one for pressure one might be marred or damaged. or the cleaner of these rollers has excessive dirt on it. it might take a few copies to find the problem. but the problem will show up. is there a mirror inside the drum area that might not be cleaned.?? good luck