How to remove white 'scuff'marks on print jobs?

This is generally due to a scratch in the drum unit. Sometimes light damage, but it's very often that the drum got scratched at some point. Take the drum out and inspect it for damage.,

In almost every case, light damage is permanent. I have had to condemn two drums for light damage ghosting on Lexmark machines because I got them used from sellers who left the drum out too long. Sometimes, they recover if you refrain from use for a bit, but very often, the damage is done. Other times, it might be recoverable, but the drum is already well run, so the odds of recovering aren't great. If the drum is cheap or you have one ready, replace it and move on.