Just bought a Berretta Elite II air gun. It says to use RWS Chamber Lube. It costs $11 for a 1/2 once. Is that a rip off, or normal, or is there a real substitute. I've seen discussions that go in different directions. Some use veg oil or mineral oil, pelgunoil, others motor oil! Seems strange you pay $55 for the gun, and 20% of that on a 1/2 oz of oil!