I'm actually using Cosmo Rotor housings with the grooves in the Rotor Housings for the single rotor, as I'm using 12A endhousings - in the event anyone was confused with my photo.

George ( down under)

 George,

Those o-rings look waaay big for the groove, reguardless of the ID. Even if silicone doesn't expand the rings shown look like they fill the groove to the point of solid lock, (read very bad). there must be some space in the groove AFTER assembly.

Bill Jepson