Hi. I am Rick. I will be your expert.
Any idea as to about how old the belt is?
Lets try reseating the belt and see if it helps.
0Open the front cover by pressing the release button at the center of the top of the cover. Then remove all of the toner cartridges (keep them out of direct light by covering them). Just pull outwards on the handles. Then remove the toner box. Next remove the imaging unit by pulling on the handle (again cover this to prevent damage from the light).
Now remove the transfer belt. It is at the top and back of the printer. To remove it, press down and then pull out. Inpect the unit for any damage. If it is damaged, replace it. Otherwise, reinsert it in the printer by pushing it in and then up. Reinstall the imaging unit, waste toner box and toner cartridges (in the correct spots). Then close the front cover.
Te belt is available at the site below and a few other places. The cost of the belt will be at least $115 plus shipping. I don't think I would invest that in it but I guess that is up to you.