Was everything thing clean???...using paint thinners or brake cleaner????
Is the head dead flat??? Is the block dead flat???
Was too much oil applied to the threads of the head bolts???....leaked out to gasket???
Was grease applied under heads of head bolts for proper torqueing???
There must have been something that wasn't right for it to leak.
Cleanliness or procedure???

just to let use all know. i fitted the head yesty with hylomar.changed the oil.tensioned everything to spec.just ran straight water and touch wood she's all ok.im not sure what everyone else uses but i just use a bit of k&h wax and grease remover to wipe the block down (after cleaning the old gasket off first) and just a bit of blackmax for the timing cover gasket. so with 156,000km and her first headgasket she seems to be driving very nice.cheers all for you responses

Hylomar is good stuff, i use it all the time