If the manifold leaks water, it will also leak exhaust gas. You really don't need an EGR system on a stovebolt engine, especially one that recycles exhaust gas all the time! The only fix for that manifold other than replacing it would be to run a piece of stainless steel tubing all the way through the heat passage and secure it into the manifold with pipe threaded compression fittings on both ends.
If you bought the manifold new, you really need to return it for credit, and buy a different brand next time.
Jerry
