Originally Posted by PaleBlueDotCitizen
In my opinion the modules sold as "sealed" units should never get dust on the sensor. If they are genuinely sealed then the dust must have been got in there during assembly.
No lens, "lensor" or camera can be "sealed" if it changes size when focusing, or zooming for that matter. The air simply has to go somewhere, so it goes in and out, carrying dust particles with it. It's inevitable.