Any leak involving a gasket, the gasket should be replaced. The problem with additives that can temporarily seal a gasket, is that it affects all the gaskets, not just the one with the problem. One typical way gasket leaks are solved is to cause the seal to swell a bit which will seal the leak for a while. However, as you can imagine, this is only temporary. The seal wears out much faster than it normally would, in fact all the seals on the engine will, since they all were exposed to the additive.. This creates the well known Leaks Like a Sieve problem, and now instead of having to replace one gasket/seal, you have to replace them all. My advice is no additives, replace the gasket.....
