Exhaust manifold/water jacket leak

I haven`t tried the epoxy , isn`t that vulnerable to heat? Regular and hi-temp silicone have not worked either. Does the Permatec Ultra Copper have a high metal content? Maybe that would do it. I`ve replaced all the studs and tried nearly every type of silicone out there but still the leak persists. I`ll see what`s available in Epoxys and check out the Permatec Ultra Copper but I`m still open to suggestions. Thanks all!