Sticking parts can definitely be an issue, especially with lower-durometer molded parts. The first thing I would suggest trying is to perform a postcure at ~350°–400°F for two to four hours after molding. This finishes most of the cross-linking that may be occurring after molding and is occurring during your gamma-radiation period in your application. An additive that helps with lubricity but may also be an issue in your application is a filler to add to the silicone. I know that Zonyl (Teflon), which is sometimes used to create lubricity within molded silicone components, would reduce sticking and cross-linking between two like materials. Generally a mixed ratio of ~10–15% Zonyl by weight is a sufficient loading. But I would try the postcure first.