Thermostat housing leaking

I use gasket sealant on the gasket and bolt threads. It is a sticky purple gel that stays soft. It cleans up with alcohol. I also used a thicker paper gasket that came with another thermostat housing I bought (~$12 ebay, looks like stainless), but I used the original chrome housing since it looked fine and flat. Some say the chrome plated housing always leak, but I haven't heard a technical reason why.