[Asturven]

The material is not so important, if you want to put really resistant O-rings you can use Viton ones, but they are more expensive and make a little diference. The most important is the right size.

Regarding the lubrcant you need an Oil with the lowest viscosity possible in order to mix very well with the air and reach all the internal points of the gun.

The oils used in refrigeration compressors are really good too.