I only know the oil by the scent. That minty smell that tells me someone has seriously screwed up. I repair air powered nailguns. They are loaded with o-rings. I know that marvel mystery oil is marketed for air tools. I still say don't use it. I say go home, find your marvel mystery oil, and throw it away.
Obviously this is a light hearted thread, and this is an internet opinion, your mileage may vary, etc. but don't put marvel mystery oil in your nailguns.
I recommend Senco air tool oil, but any company that manufactures nailguns should also sell lubricant. I think it is basically 10 weight non-detergent.