Update;
I've removed the bag and the connection pipework and the bag was fine....however... the topmount turns, when turned one way no air can escape, when turned the other air leaks out from the top .
I think that the seal is breaking under the top nut(which I cant undo).....I've ordered another bag and strut so hopefully when this is bolted on it'll cure the problem.
Just wondering, where does air get released from if you lower the suspension for example?....from the bags themselves or the valve in the drivers wheel arch?