We're having issues with our Ricoh Aficio SP C830DN. It's been printing smudges and marks on everything, usually in a repeating pattern. It appears as a black or dark colored mark on lighter areas, as well as a light mark on darker areas (like the below photo of a field of dark blue with a mark through the middle). It does not seem to be a toner issue and we're not sure what to clean or replace to solve this problem. We recently replaced the black drum. It's been suggested that we need to replace the fusing unit. Could that be the problem? Looking forward to receiving any advice!