Let's not jump to conclusions here. Don't just buy a head gasket, take the engine apart and throw it in there. Once the head is off, take it to a good machine shop and have it pressure tested.

Has the car had regular coolant changes. If not, it is very possible that the aluminum head has corroded through between the water jacket and combustion chamber.

The good news is that these cars respond very well to head work. With that mileage, don't even dream of putting the head back on without a fresh valve job and valve guides.

Good luck,