Canon IRAdv 4235 spots

[Will]

Have intermittent black spots on the copy of a Canon IRAdv 4235. Checked and cleaned both the drum unit cleaning blade and charge roller and can't find any issues. Customer is using OEM Canon toner. Tried a different grade of good quality of paper which makes no difference. Fuser seems to be fine nothing found there either. The spots are random and have no pattern and are only few here and there and not excessive, but enough that the client is complaining about it. Looking for suggestions.

[slimslob]

With Ricoh that was an indication that the drum was worn out, especially if it first started toward the front and back of the drum and then expanded inward.