DuPont sued several companies, including Slick50, to force them to quit using PTFE in their formulations but lost. The FTC jumped in as well. There's a link on this page to the FTC lawsuits and findings. http://www.carbibles.com/additives.html
IIRC there was at least 1 lawsuit involving an aircraft engine which seized in flight, the oil passages were found to be clogged with PTFE particles from the Slick 50, but I can't find a link.
Anyway, ATF is an old lifter cleaning trick. Used to be, you changed the oil, replaced 1 quart of oil with ATF, drove it to the next oil change interval and the lifter noise would be gone. BG used to sell a two part engine flush (it smelled like Pine Sol) which really did work on lifter noise.
Subaru center diff plates were known for chatter in turns, we had several come through and decided to try a transmission flush on one, just for the heck of it. Damn if it didn't work. Our theory was the solvents in the flush chemical (again a BG product) cleaned oxidized fluid off of the plates in the center diff allowing it to 'slip' smoothly, as it was designed to. The same thing happened with the newer Quadra Trac Grand Cherokees.
Seafoam will definitely remove carbon etc and as Lesley pointed out make a big ol' stinky cloud. ATF will work as well. We had the police show up at the Isuzu dealer one day because the Seafoam/ATF mix cloud from our shop had rolled out into the six lane road out front.
Water will definitely remove carbon, yank the head off a car with a blown HG and the offending cylinder will look like the day it was born. That's known as 'steam cleaning'. I once did a CB350 Honda that way, pulled the airbox boots, revved the engine and sprayed water in the intakes. The amount of crap that flew out of the pipes was amazing; there were actual flakes of carbon.
I once took apart a nice quiet Spitfire diff and found pieces of a small block Chevy cork valve cover gasket in it. Cleaned it all out, filled it with 90 weight and put it back in, sure enough it howled.
Oil stop leak products are bad news. They soften the seals etc and may work for a short time but the seals will wear much more quickly leading to bigger problems. Also it is not selective; if only 1 seal is leaking the stuff will affect EVERY seal in the same way, oops.
I saw a Ford automatic disassembled at the AAMCO I worked at, when a piston was popped out of its drum the piston external seal literally flew out of the groove and expanded to probably 1 1/2 its intended size. The trans builder said that was because the stuff worked by softening and swelling the seals. FWIW, the stuff that came out of that transmission smelled like brake fluid to me.