Do you know of a UK supplier of GASGACINCH gasket sealent, their US part number is 440B for the 8 oz size, its the one you apply to head gaskets before fitting. I googled it but so far came to a dead end.
I guess it depends on the application i used to use Gasgacinch on copper headgaskets but found hylomar or best of all the Loctite spray sealer even better , my tub of Gasgacinch sat on the shelf for years unused