If the fuser unit is beginning to fail, the unit will still adhere ink onto paper but the ink will be smeared and areas on the paper will be dirty when it exits your printer. If the fuser unit has ...

5] Dirty or damaged fuser Laser printers put the toner permanently onto the paper by using a heated roller called a fuser. Over time, the fuser’s roller can become damaged or have toner caking ...

It's the drum/OPC belt (whichever the printer has). If it was the fuser, the ghosting would be every 1" or so, as the fuser rollers are smaller diameter.