Thanks for the product advice Norman, I went through the whole range of about a dozen gasket and silicone compounds but all of them said 'Not recommended for head gaskets' I will look for the one recommended, cheers.

Incidentally, does anybody know how hot the head gets? Some compounds are rated at 260 degrees Celsius, I am guessing that it would get much hotter than that.

Seems to be sealed fine without a gasket so far