Tap-a-Draft Help

I have a tap-a-draft that will not hold pressure and am asking for some help in troubleshooting the causes.

I picked this up used and gave it a good cleaning. I pulled the spout out and the diffuser tube. All of the seals I replaced and took it as far apart as I can to give it a good cleaning. When I u[put a gas cartridge in it I get a bit of bubbling in the bottle but most of hte gas escapes out the front of the regulator. I know there is a relief valve in the thing that prevents excessive pressure and i believe that is the black thing on top. After about 15 minutes I have gas escaping through the spout and in about 30 minutes all of the pressure is gone.

So far it has cost me a bottle filled with Orfy's Mild so I switched to just water to try ot figure the issue out. If anyone has a had similar experience I would sure appreciate some advice on what might be happening with mine.