[smokes]

Is anyone running x rings? could you let me know what part no's they are?

Please note:From a engineering perspective o-rings are not that great at reciprocating sealing at high speeds as they roll x-rings are better. Also because the o-rings roll they need a toleranced groove that stop the rings distorting. The Plastic spacers are not stiff enoungh for this role.
For good vacuum sealing the suface finish must be between 0.8 and 3.2 ra or the gas will find a way in. It is achieveable on plastic but the shaft spacers yokomo provide are closer to about 32 ra. The nitride coating is dependant on the surface it is coating if the shock shafts are cold drawn the polished before coating you should get a good finish of about 1.6 ra. but I suspect it not as it quite expensive to achieve these surface finishes on such small parts.

I guess what I am trying to say is unless you are willing to design the parts to meet surface finishes and groove tolerances required for vacuum sealing applications. You won't stop gas leaking back into the shock. And the solutions above will only slow the rate of vacuum leakage.