Quaker State high mileage use to contain slick 50. I used it in my old Pontiac sunfire I had in high school and college. Beat the [censored] outta that car when I was a teenager and it never burned a drop of oil.
The Quaker State "Slick 50" was very different and contained no PTFE. It was basically a thicker base oil fortified with a lot of conventional additives and detergents IIRC.
So it's not so much snake oil as it was/is overpriced swill... I've used the QSHM with 50 in it without hesitation (bought at Ollie's Outlet) but would not buy a separate bottle for the asking price...
Slick 50 also had a gear oil additive in a small 1/2 pint bottle. I added some to the outdrive on by outboard boat engine. Never had reverse after that. Too slick for the reverse set up those outdrives used. no reverse even after several flushes and oil changes.
Back in 1989 or 1990. My dad had bought a old Honda. I don't remember the model, just that it was blue with four doors and a 5-speed. It was a great car, got 30+ MPG. I'd changed the oil and put some Slick 50 in it. After that it started getting 35 MPG on every tank. There was a clear improvement in how the car performed.
Now, the trade name "Slick 50" has been bought, sold, litigated, and such many times. What's the bottle these days is nothing like what the original formula was. And most everything out there is snake oil.
I use Archoil 9100 in my 7.3 diesel with HEUI injection. That stuff is pretty good for those systems.
I found 8 or 9 bottles of the old synthetic PTFE version at Ollieâ€™s like two years ago for $1 or 2 I bought them for novelty purposes. Also found a bottle of greased lightning ptfe additive. Not sure what Iâ€™ll ever do with them but I have them. You can easily buy micron sized PTFE powder from China on eBay and just mix it with oil and grease if you want to experiment with it.