This has happened to me so worth a check.
When attaching the toner motor back onto the toner bank I for some reason unknown to me didn't attach it properly and it slightly buckled the back end of the toner bank frame. I removed the motor and re-attached it and it worked fine.
Have you checked sp mode 2972- Toner suction collection bottle operation time? If it has exceeded 580/600hrs you will have to reset to 0 hrs.
A few of the posters were sayng about the toner collection bottle sensor. It does sit in a poor area without any cover allowing toner to fall from the chuck areas.Usually the seals fail in these toner banks through time and are easily replaced but if you don't want to go down that line as you maybe a fitter instead of a fixer replace the toner bank
