The three main causes of printing issues are toner cartridge, photo conductor, or the Fuser. The easy way to narrow down the issue is by interrupting the print process as the paper is midway through the print cycle by opening the access to the toner. Look at the paper to see if you see any marks. If you see marks on the paper before it enters the fuser, then the cause is most likely the photo conductor or possibly the toner cartridge. If the marks only appear as the paper exits the printer, then the marks are made by the Fuser. The fuser is the part of the printer that gets really hot and is located just before the exit rollers (usually with an access door at the Fuser to remove paper jams.
You can remove the toner cartridge and very carefully pull back the cover over the photoconductor to see if you see similar marks matching those on the paper. You do not want to touch the green/blue roller and you want to minimize exposing the photoconductor to light. It has been a long time since I worked on this model and I forget if the toner cartridge on this model has the photoconductor as part of the toner cartridge of if the photoconductor is a separate module.
You can also open the access door at the end of the paper path to see the Fuser. The Fuser may also have its own access door (it has been so long that I forget what the Fuser is like on this model). Just be very careful to let the Fuser cool down or you can get a dangerous burn since the Fuser is extremely hot! If there is no access panel on the Fuser as well, then carefully look at the orange rollers on the Fuser (you may only have a very narrow slit to look through). If you see marks on the orange Fuser roller which match the marks on the paper, then the Fuser is defective. Sometimes one of the Fuser rollers will start to peel apart which can also cause marks. Most times the edges of the Fuser rollers are most likely to have marks, but the center of the roller especially on this model can have marks from the heating element.
