I haven't vacuumed dev unit at all. Everything was fine untill tonner hoper was empty..
All day I was examining BSI notes in Webespos. Find one note about "image fogging when toner is near empty"
Note says that if fogging happens everything must be cleaned, then 08-445 must be set to 4 (less new toner added) and 08-446 to 1 (more recycled toner added). If new toner hopper is to the end there's almost no recycled toner in recycled hopper also - machine just asks for toner instead of "eating" it from recycled hopper and making "stress" for auto toner sensor.
As a reason - low quality paper was mentioned. As I understand, dust + recycled toner changed toner parameters enough to make a lot of mess.
At the moment quality looks fine..

Time will show if it was the root of my headache.. Let you know if smth..
