I don't know what the active "ingredient" is in Dexron type fluid, but in the days of old {type F, etc.} the magic component was nothing more than mineral oil. They put the red color in it so a mechanic would know if the transmission ever ran hot. It would turn brown and smell funny. I don't know what one would gain by using it on a gun. I like RIG grease myself. As above, guns really don't need much as far as lube is concerned, but where they need it you had best have it. A prime example of this is the Winchester Model 12...you better keep the end of the action bar greased good or the little tab that locks the bolt will wear and then the gun blows itself open when you fire it.
Personally, my guns need more rust preventative than they need some type of special oil and I find that RIG grease works the best for that too.