Can't help with that, Snapper. You'll notice I said nothing wrong with the Marvel Mystery Oil "as far as I know". Perhaps I should have explained further. I've known a lot of people who claimed to never use anything except Marvel Mystery Oil and never had a problem. But the possibility of damaging the seals and o-rings is the reason I stayed with oil sold specifically for air tools. I owned a brad nailer, but never repaired or tore down any of them. However, quite a number of automotive air tools have small pressed in oil seals almost identical to the ones used in the hubs for auto wheel bearings (except much, much smaller). Those can wear out and leak causing a considerable loss of power. In addition, many, many automotive air tools (especially impact wrenches and ratchets) use small rubber or plastic (lot of variety in composition and size) mushroom shaped throttle valves. It was very common to find those crumbled and/or melted. If caught early (when they started leaking a little), they were very simple to replace, but in a lot of cases, that crumbled material was then blown into the air motor where it either locked it up or they melted on the inside of the cylinder requiring complete disassembly, cleaning, honing, and replacement of the vanes.
Now many of the air tool manuals "recommend" occasionally running a tablespoon full of "solvent" through the air intake, followed by air tool oil. I used Varsol and never had a problem, but I suspect a lot of mechanics used some kind of solvent that melted those throttle valves.
Air tool oil itself is supposed to be a "gum solvent" oil and I consider it to be cheap; so why not use it and be sure? /forums/images/graemlins/wink.gif