The best head gasket repair is.......... A new head gasket.
Each type of head gasket sealer is specific to the engine as it has reinforced pieces of metal at the points required. The is no paste, glue or any other magic that can stand up to the pressure for any reasonable length of time. What will happen is that when it fails it will do so spectacularly and WILL lead to a large bill to repair all the internals of the engine when the very large bang tries to fire the Pistons and other internals through the hood of your car.
What is the best head gasket sealant?