the 3 in 1 thingy used to cause a bit of a panic with the most paranoid of people ( theres another thread sumwhere about oil and high pressures, can make things go boom boom) but it can happen with other oils aswell so nvrmind. Other oils have funny reactions to O-rings and turn em into the size of tractor innertubes but im damed if i can remember which do what. although im prolly gunna get heckled now with accusations of an intrest in kinky sex but vasoline is good (in moderation) for bolts, movin parts etc. But i would personally use silicone spray cos it A: does a bloody gud job B: dont have to keep putting it on ur gun...
hope it helps
p.s look at what silicon does for womens breasts for god sake ;-) i rest my case