Leaking transmission fluid

My SUV had a leaking lower radiator hose. I had put it off until I could get to it. I had just been adding water. I changed hose took for test drive and found that the lower transmission line going into radiator was leaking from the bung that screws into radiator.

First question.

Can I just change the bung on radiator, or do I need a new radiator?

Second question.

Do you think the radiator is just worn out? Radiator was not that old.
Or is something causing pressure to build up and cause the leak? If so, what could be causing pressure build up?