JD 420 - oil leak around PTO shaft

Hi,
Newbie here. Grew up farming on JD's, now I own my first. I purchased a 1957 JD 420T to restore/move snow/etc.

I have an oil leak around the pto shaft. It doesn't drip when not engaged, but when engaged there is a slow, but steady, drip. I'm hoping there's just a seal there to replace. I'm not hesitant about diving in, just wondering if someone could help me out with what might be the cause and what I might be facing prior to jumping in.

Thanks,

BA