^I know it was brought up before. Basically a spray-on K-mod. You'd put one balloon over the PC and spray that stuff on it. I don't think anyone actually did it though.
As for making parts, you'd need some kind of mold first, no? I'd think that 3D printing would work better if you had access to it. This stuff could perhaps be used to cover reservoir leaks, but those are rare. For pressurized components, it's definitely a better idea to go with water weld or marine epoxy or something.
Also, "as seen on TV" products tend to be rather untrustworthy, haha.