Are you aware that the gaskets go on the stock plate and the 90* adapter in a certain order? The paper one and the cork one have to be in the right place, or it will leak. I forget what order they go in but if you don't get them right.......leak.
a real,long shot try to wrap it with pipetape 1nce , clamp a hose on it over the weekend and see if its leaking , might tell you a little more of the story