72 Demon new Proportioning valve/Dist block leaking

As for cooling, it's not the same as carbon steel. You can either let the copper air cool down to room temperature, or drop it into cold water - either way, it will be dead soft, and ideal for re-use. I prefer dropping into cold water, as that knocks off any surface scale from the heating process. In fact, it might even be better than new. Punching washers out of sheet copper tends to work harden them round the cut, which is why I always anneal new copper washers and gaskets before use.