Tried it once with the male coupler on our Case 430 skid steer.
If I remember right, there were several seals inside, an O-ring, a flat rubber seal like a hydraulic piston uses, and a plastic ring. I replaced the O-ring but it still leaked, couldn't find any of the other seals.
I have never had a female coupler apart. I'm not sure that you can get seals for them, if you could, and they weren't too expensive, seems like they would be worth rebuilding since they aren't cheap.