Lately I'm hearing some remarkable things about Marvel Mystery Oil used as a fuel additive in aircraft, from a VERY experienced and competent mechanic and aircraft owner. (I've read positive evidence from others who are using it too, in everything from lawnmowers to bombers.) Presumably this is not technically an authorized (i.e. legal) aviation product, but based on his testimony I think I'll start using it myself in my P&W-powered warbird. Anybody else out there using it and care to share thoughts or experiences?