Transmission cooler connection.
This may be "made onto" the rest of it, inside the radiator.
If your radiator is old (internally has mineral deposit restrictions)/ this line you describe broken or damaged, maybe it's time for a new radiator?
In my searching for you, I found some over $150.00.
To my surprise I found some really reasonable!
Check out my screenshot below from "Rockauto".
Monday, April 20th, 2020 AT 4:14 PM