Water Valve Assembly

They are made as a sealed unit, and can be replaced with a multitude of other valves from a lot of other cars since it's a vac operated type.

You might run across a working original if that's what you want also, but most of them leak coolant after all these years.
I would feel it was a half miracle if I found one that worked AND didn't leak.

Ha, a half a miracle just happened. :D