muffler patch stuff

getting my exhaust pipe gaskets tomorrow cause my old ones are leaking and was wondering about that muffler patch goo they sell at advanced auto im thinking about using it with my new gaskets kinda like permatex-ing them on there with it good or bad idea? will i end up fubar-ing my 340 manifolds? eventually i want to put headers on and sell the manifolds
any advise?
thanks
Terry