Two things: check your orings on the post, make sure they're happy and not scarfed up. A cut in the oring could mean beer seeps past it, and you lose both beer and co2.
Second, and I've had this personally, flat blade screwdriver and ensure the top of the disconnect is screwed down all the way. I had one that was shipped to me slightly unscrewed for whatever reason and beer would seep out the top of the disconnect.
Also, there's an oring inside the disconnect (unscrew the above mentioned disconnect big fat plastic screw thingy on top), if that's all wrecked it could cause a leak.