Faded streaks on printout

I recently purchased a HP Color LaserJet 4500n (used, obviously.) It was shipped with all toners installed, so there was quite a bit of spilled toner in the machine. There were pages included that were printed just before shipping, and they look fine, but now it leaves faded strips along the two long edges of the paper. All colors are faded, so it’s probably not the toner.

I’ve tried cleaning it, with no change. The readout claims that there should be 70% of life remaining in the drum, and the drum looks fine. Any suggestions to correct the problem?