One color or different colors? If the dots are a distinct single color that matches one of the cartridges then likely you have a bad cartridge (an error like a dead spot on the drum) that cleaning is not going to fix. If the dots are evenly spaced you can consult a repetitive defect chart for your printer to see what component is bad.
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Multiple colors. It looks like the transfer belt has spots of color on it. I've tried to wipe it off after removing the toner cartridge tray but it didn't really help. Nervous to attempt removing the tray from the back (as seen on YouTube).
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