Coolant leak, quick head gasket fix?

What is your question?

I have a Mazda E2000 from 1996, it has a coolant leak, that goes into the combustion chambers as the mechanics said also during the night it pours in the paviment under the drivers seat. Replacing the head gasket is really expensive but I'm wondering about this products that you directly put into the radiator and it fixes it at least temporarily. In my case should I use the one for Head Gasket repairs, or the one that is especially for Coolant leaks? Or maybe both? I'm a bit lost here. Btw I'm in Australia at the moment as Im speaking about the stuff I can buy here somewhere like Supercheap Auto. Thanks!!

How long has your 1996 Mazda B3000 had this problem?

3 weeks