you shouldnt really use sealant on a headgasket there isn't a need for it unless, you have a metal gasket without a rubber coating, but if the metal gasket doesnt have a rubber coating then it should have rubber strip round the oil and water feeds and round all the other important areas to stop leakage.
you shouldnt use sealant on headgaskets it may block oil and or water hole as it is compressed downwards. metal headgasket or not no sealant should be needed, personal experince tells me so