It is not an easy task.
I did a wash of all my cams earlier. Pec pads (anyone remember?) and iso Propanol is the right stuff. After 4 tries, there is still stuff there (while the Sony cams are sparkling). The good news is they seem to be moving around.
Will have to go through few more cycles, I guess. This time I am going to do it in portions- half a sensor at a time.