presumably sprung a leak, not common these days but maybe a manufacturing glitch I wouldn't be too concerned but if the new one also fails this quickly then I'd look for other issues in the cooling system.
If it is a leak, have you tried Radweld, I once fixed a leaking matrix heater with it, that would otherwise necessitated removing the whole vehicle dashboard.
If it's just a minor leak, then as Hymie suggested, try Radweld .... it's amazing stuff and dead easy to use. You just simply add it to the radiator when it's cool, run the engine for approx 20 minutes, then cross your fingers and hope it's done the trick :)