Yeah, I used some once!
Along in the early '70s I bought an International, 2 axle cab & chassie, 4 x 4 at surplus. It had a 265 in line 6 gasser, W/air on it, had great rubber (8.25 x 20), and had had a12' flatbed on it with an Arctic grade canvas top. It came from Eielson AFB. I guessed that it had hauled stuff to the flight line, as it was blue. When I went to pick it up, It wouldn't start, but I knew the engine cold. I pulled the valve cover & somebody had backed out a couple of exhaust valve tappets all the way/ I made adjustments on the spot/& drove it away, not thinking too much of the blue smoke. After tune up, the addition of 5th wheel for 28' semi-trailer, etc., I took off down the AlCan for a load of stuff in Dawson Creek - 3100 miles round trip (back when the Road was fun to drive), camping as I went. It ran perfect, but it became abundantly clear it was using excessive oil, & I was desperate for some remedy, after a couple hundred miles......(if there was one)... I started using STP with the oil. Had to stop at about every road house for STP & oil. Total was an honest 17 gallons of oil & probably pushing 2 gallons of STP for the trip - but I made it. I do believe the STP cut down my oil consumption some, but who knows? Later that summer & did an "in frame" in the yard/found no taper in the cylinders, honed heck out of them, ground the valves & got 100,000 miles out of her.