Yes: STP, Rebuild In A Can, Marvel Mystery Oil, all snake oil.
The one place STP is good for: old, sloppy American gearboxes. Also predicated upon warm climates!
Yeah, in a way.
A couple of decades ago, the transfer case in my lumped 56 Willys 4x4 pickup bit the dust. Classic failure. the gears got so loose so as to climb on each other. I was lucky to find a NOS unit at a Jeep place in a nearby town.
Not hard to pull the old. What I and helping son did not know, was that the transmission gear set needed to be secured in place. It moved and needles fell tot he bottom of the case.
With dexterity and energy that I had at the time, I was able to fish them out and put them back where they belonged. At least, I thought so.
Got it all back together. But, the transmission was stuck In low.
Added STP and tried again. Why ? Logical, not so much. Desperate , for sure. Amazing, another try, and bit by bit, the box loosened and shifts returned to normal.
So, STP ? Onl;y in desperation.
Carl