Lubricating pneumatic gun - what oil?

[spoolin01]

I decided to dig into a Mares Frontiersman that doesn't hold air and had been sitting around for a few years. It's the same length as the gun I use, so I wanted to prep it for a backup. I used silicon oil a few years ago in a couple of guns, but in looking at a Mares service manual, it says to use SAE 10 hydraulic oil, like Mobil DTE Light. From what I can tell, that's a mineral oil.

Which should be used, silicon or mineral? The o-rings were so hard at first I thought they were plastic - could that have been the choice of oil that was used?

[mitsuguy]

I would use whatever they recommend...

O-rings will get hard like plastic over time and actually you are better off using it more often as this will keep them lubricated and soft... Kinda the same reasoning why a reg that has sat in a closet for 2-3 years is probably in worse condition than a reg that has been used regularly for the same amount of time...

[spoolin01]

I guess I've never had a reg or other device that was old enough for o-rings to get brittle hard. I've seen them crumble, but never snap! It turns out this gun may be 30+ yrs old.

I found some 5W fork oil at the local motorcycle shop...