Like they say, there are a hundred ways to skin a cat. I'd say the gasket-maker alone might work, but let it cure for a couple days before refilling the coolant and running it. A 100% sure-fire way get rid of t-stat leaks is to spend $75 or so and get a real billet aluminum housing (not cast!) that uses an o-ring to seal. No gaskets or sealant required. But it's not for everyone.
