1987 for Mustang 5.0 Radiator valve? Stem? Sandwich plate? Plug? 2024-12-27

Hello all! So I found a leak on my 87 stang. I traced it from the ground all the way up by the radiator cap. The little valve stem (Not sure what you call it). It was leaking from that part and slow dripping all the way down the radiator to the rail to the ground. The steel valve has a clamp on it and was so loose with threads showing and not tighten all the way / bent. My stang has no reserve I believe a hose would hook to the valve for the reserve tank. Does anyone know what’s this part is called? and what it does? I looked on mishimoto and can’t find the exact part. Thank you!