Mine went a few yrs ago and cost �350 to repair by a Mech I knew - expect a dealer to cost more.
Have had 5 Nova's,Corsa's and only one head gasket went them - but seems to be common enough with the Pre 2002 Corsa's/Astras.
Causes ? Mine just decided to leak and I didn't realise the water level in the coolant bottle had fallen due to a " tide " mark inside the bottle and damaged/melted a couple of valves in the process.
The gaskets are made of silicone these days and if not properly fitted to the car the will leak after a certain time.
�45-�50 per hour at garage and will prob take upto 8 hours.
some corsas have the older style vauxhall engines (non ecotec) and these are common for water leaking into the oil which is easily identifiable by the emulsified engine oil on the filler cap.