Nope, not transmission fluid. It is Mineral Spirits 20-30%, with Napthenic Hydro-Carbons 70-80%, and Chlorinated Hydro-Carbons 0-1%.
With of course the secret ingredient that makes it smell so good and makes you always want more!
http://www.turtlewax.com/res/msds/MM010-4.pdf
Edit: Lubricity wise, it's not all that great. Going by a independent diesel additive lubricity study, Marvel Mystery Oil made no significant difference in the lubricity of Ultra Low Sulfur Diesel. So it probably has about the same lubricity properties of ULSD diesel. Still more lubrication than gasoline though!