I tried a generic drum & generic toner - and it prints dirty.
I also tried cleaning everything per the instructions in the documentation.
Could it be a faulty drum unit? Or is it just a generic drum unit issue?
I am about to buy a new drum unit, and don't want to buy generic if it will always cause this issue.
P.S. I tried new toner cartridges (generic, but I know these work with a 'genuine drum' properly).
Edit 1: This is a scanned image of a sample print-out (redacted for privacy purposes):