I have heard the Marvel Mystery Oil stories about freeing up stuck valves. I use it for freeing rusty bolts, and it doesn't stink as bad as some of those other rust blasters. It smells like root beer or sasaphras to me. Haven't tasted it yet.
What about those info-mercials that sold those oil additives where they would put the additive in the engine, drain the oil out and then run it around a track in the middle of the dessert with no oil? I can't remember who it was, but they had a retired Indy 500 driver promoting it. Mighty snakey looking, but how did they do it?
