Well that aint actually the mote Gary that is the pinched section of the O ring
(I dunno, country kiwis
) If you look closely you can see the two pinched sections and how the sectionn between doesn't follow the line of the ring. The section between was protruding inside the chamber.
Here is an example of the frosting after it has started to sublimate and you can see the dust mote near the center top of the image