I have no doubt that many will ring in here with their praise-jesus stories of how one miracle goo or another saved their engine, or engines, or every engine in their fleet, or whatever. Along with a few stories about how one bottle of miracle goop ruined their zillion-dollar race engine or some such.
Stories is stories. Anecdotal evidence isn't worth the paper it's written on. The only thing that could possibly be meaningful is, say, a fleet manager who ran 25 vehicles with straight
oil and 25 with miracle goop added, then kept meticulous records about engine condition over a long, long time. I've seen very few field tests of that caliber; at most we get a serial story about one truck that ran forever and one that blew up the first time it had an
oil change. Not meaningful.
Whatever good Marvel Mystery
Oil, Slick 50, etc. might have had decades ago when oil formulations were simpler and there were far fewer choices, I think a moment's thought will show that there's no need for any of this stuff any more except *perhaps* in some very specialized situations - hot street and race engines not included in that group.
Oil companies have spent billions of dollars formulating their products and meeting increasingly difficult wear, breakdown and longevity standards in just the last 25 years or so. If there REALLY was some mystery miracle additive that greatly improved oil performance, don't you think they'd have evaluated it and either passed it by as not useful or included it (or some more sophisticated alternative) in their current formulations? Do you really think that every oil seller would market a product obviously missing some miracle ingredient?
Nah. However smart Mr. Marvel or your grandpa or your clever uncle the mechanic might have been 40 years ago, I think oil additives are a moot point, or possibly an active negative, in modern oil. Watching the formulation for older engines (old, or old-tech) as in watching the
zinc level is one thing. There are certainly better formulations for one engine and one purpose or another.
But the notion that there is one magic goop that makes oil fabulously better for all engines, or any subset of that idea, is obvious nonsense. Don't waste your money once you've chosen a suitable, quality oil for your engine and purposes.