[johnwalkr]

In addition to the other comments, in general o-rings are actually very difficult to use for vacuum sealing. Unintuitively, at least until you have some experience in seal design, lower pressure differentials are much harder to seal than large ones. They depend on the pressure differential itself to form the seal, they don't work like a gasket between 2 faces. This is also why compressing in a v-groove doesn't make them perform better.

Even if you can get an o-ring to seal a vacuum, it will likely only work in the context of applying a vacuum to a system to a desired level, not as a permanent seal.