If the problem is not solved after printing a few pages, the drum unit may have glue from label stock on the OPC drum surface.
Clean the drum unit as follows:
Position the print sample in front of the drum unit, and find the exact position of the poor print.
Turn the drum unit gear by hand while looking at the surface of the OPC drum.
When you have located the mark on the drum that matches the print sample, wipe the surface of the OPC drum with a cotton swab until the dust or paper powder on the surface comes off.
Do not try to clean the surface of the photosensitive drum with a sharp object, such as a ball-point pen, and so on.