Leaking oil drain valve - please help

[Lollygagger]

I just changed the oil on my Turf Tiger II and now it’s leaking from the spot shown by the arrow in the picture. It’s a very fast leak and still leaks when not in use. Any ideas what went wrong or how to fix? I found the part online but it seems like it should be simple and probably shouldn’t have failed in the first place. The leak is not at the engine or at the drain, but from the area where you put the wrench.