The normal place for a gasket to go is above the rearmost core plug on the exhaust side, especially on 2wd(heads) as water ways different shape, and gasket not supported as well as a 4wd one.
If losing ONLY water, not performance, and no water in oil then it has obviously gone outwards so sniffer test will not show anything, where abouts Norfolk are you, as some other people could have a look/help see ?
tabetha(norfolk)