Answer:
The answer to this simple question is NO: Thermagasket do not do what it is claimed to do! After dealing with this company on several occasions I can truthfully say the product is a ripoff! I'm sure most readers will judge this as a very strong statement, and in fact it is so allow me to explain:
I am a professional mechanic: certified by Jaguar, Mer Benz and ASE I've built and restored cars of all types all my life. I also own a car dealership and deal with car problems daily.
Last year a Cadillac with a North star engine became a serious problem. Great car but suffering from overheating. All tests suggested a head-lifting problem due to speed related combustion pressures and a terrible cooling system design. I used the Internet to gather information; there I found the Thermagasket ad. It sounded wonderful, so I called their number and talked with a tech. rep. by the name of Dave. He explained -- drawing from his years of "solving North star cooling problems" what was causing the overheating problem. Of course he claimed Thermagasket was all I needed and it being guaranteed why not try it.
I ordered the kit he recommended. I used it exactly as instructed. It failed to solve the problem. I called Dave. He suggested a long list of things to do. Each amounted to spending more money with Thermagasket. Mistake! Nothing he or others (once he would no longer answer my calls) suggested worked. The Cadillac was "Not Repairable" or so Thermagasket's president added. How could a business market a product that is worthless? I guess profit drives them.
To be fair with Thermagasket I tried their product on a second vehicle: 2001 Honda Accord, 4 cyl engine. I'd judge this a very common engine and, as Thermagasket counseled, one easy to fix. Ordered the product. Used it exactly as instructed. It also failed to fix an overheating issue. I again talked with the experts at Thermagasket but they failed again.
The obvious conclusion -- Thermagasket does not work as advertised! Save your money -- don't buy it!