leaking trans line at radiator help

[1911a1]

ran into major stumbling block when I was trying to break in my new engine. The trans input line leaks badly at the radiator.

I will try looking closer at it and look for burs on the line flare.
Not sure what I can see on radiator bung except to try an inspection mirror.

One other problem is the old flare nut on the line has about had it.

If I have to repair what do I need to track down to do it. I've done some searches and I seen references to "barbed flares' to make sure the rubber hose doesn't come off. But where can I get the new steel flare? is it possible to use brass? And what tools do I need to do it.

Appreciate any help I can get.

Thanks