CQ cs-2550 light prints

have done all the cleaning of the mirrors changed out toner motor changed out both boards and even the dev. unit
can run dev install and will work for a couple of day and then it will come back to light streaks pull the dev unit out and it looks as though there is no toner on mag where streaks are
this is when you run prints wish does not use the mirrors, run Statius page and there is streaks run dev install and looks great
what gives?