Were you able to determine what the cause of the horizontal lines was? I'm having the same issue with a 3260. The lines are printing exactly 3 inches apart on every page with my printer.
The link that the support person provided suggested buying a new toner cartridge, but I'd rather not waste money on that if the problem is more serious.
Here is an article that will give you some steps to try and resolve the horizontal lines. If you are still having issues after trying these steps, I suggest that you call into our support department for assistance @ 1-800-821-2797 or 1-800-835-6100
I have a Xerox WorkCentre 3215.
Printouts have horizonal lines that fade in the middle but seem to be fairly consistant from one printout to another. I have replaced the toner cartridge and cleaned the drum and anything else i can get to but no change.