Use pure silicone anywhere O-rings slide on something. Silicone oil for dynamic O-rings...those that slide like a bolt or breech O-ring, fill probe O-rings, etc.. Silicone grease for static O-rings...aids with assembly.
Silicone oil is sold inexpensively as "silicone shock oil" for RC cars. Silicone grease is sold inexpensively as automotive dielectric grease.
Not only is silicone an excellent lubricant for O-rings, it is also non-combustible.
However do NOT use silicone where metal touches metal. It is a terrible lubricant for metal on metal.
SuperLube synthetic grease is not a silicone-based lubricant and it is extremely flammable. It is good for metal on metal.
Note you don't want either oil or grease on a PCP hammer if you can help it. The changing viscosity with temperature will tend to cause velocity swings, and it can also cause a vacuum or air cushion symptom in some PCPs. Better to deburr and smooth the hammer and tube and burnish in a dry lube like graphite, molybdenum disulfide, or tungsten disulfide.