Problem solved.

The problem was that the new o-ring inside the female coupling was very stiff, and was damaged upon installation. It was kinda sheared off by the male coupling. The trick was to pre-stretch the o-ring a bit to have a larger inner diameter and to grease it up good. It also helps to leave the wire clip in the closed position - it will stretch then snap into place with a click when properly seated.

I did buy the Lisle 37300 tool. It wasn't big enough to fit over the pipes properly, but I was able to get enough of it seated that it worked.