Drivers header leak

I’m need recommendations on what to do to fix a leaking header on the drivers side of my 360 duster. The headers are cheap hedman that I bought from an individual who never installed them in the original box. I know they are not dougs or TTI but I used copper gaskets at the head and the collector but the drivers side will not seal up. I’ve changed the gaskets twice now. Is there any exhaust sealant that Anyone has had success with or should I be on the hunt for a set of Dougs or TTI headers for the car?

thanks Jim