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.
The female is the one giving me trouble (insert joke here) and I can't for the life of me figure how to disassemble it. The only fastener I can find is a hex head cap screw accessed from the rear inside of the coupler. It spins the smaller diameter disc in the middle of the face when you turn it, and I've yet to be able to hold the disc still. I'm going to pick up some new ones after work ($105 for the pair) and will get serious about tearing them down once I have the new ones in place.
Thank you. I tore the male apart last night and it was pretty simple, only had one seal up near the front (U-shaped PTFE from above). Didn't have a chance to destroy the female coupler yet, but I'll get to it. Got a new set from the NH place yesterday and put them on last night, so it should be good to go. If the originals lasted 25ish years, so these should see the machine out.