The image below is of a blank A4 page apart from a few crop marks. You will see that there are grey artefacts over the whole page. The horizontal position and intensity of these marks varies from one printed page to the next and have been getting worse over time. They are not scanner artefacts because they are produced when pages are printed from a computer. They are not specific to any PC particular software being used. They are always grey irrespective of the amount of colour no the page.
I done basic cleaning of paper transport rollers but I have shied away from too much rummaging around on the "drums" and "belts" inside.
This is a personally owed printer discarded by the company I work for and has put in good service through the years. Obviously I don't have a service contract.