Thanks both for infors, cos my current 50D mod with transparent glass replacement and there are dust between replacement glass and sensor. I plan to give it a cleaning, your case might work to me too.
I remember there's a rubber grommet that holds the glass in place, should be the same with the Canon, this being so it be unlikely for dust/dirt to get into the space between the glass and sensor. Try cleaning the glass surface that is facing the lens and shoot & check. Hopefully the dust is there and you are able to clean it off. otherwise, the cost is expensive (I think) to send it to professionals to remove the glass to clean the inside surface and sensor. All the best.











