My Disco has lately been loosing the air from the rear suspension bags when parked. It replenishes when I start it, so I know it is not the compressor. It will also stay raised (even for days) when I raise the rear and then park it, so I know there is not a leak in the bags themselves. I believe it has something to do with the relief valve (or whatever regulates it under normal "leveling/parked" actions). I'm hoping I don't have to replace the entire system, but don't really know where to start. Yes, the entire system is probably worth more than the vehicle itself, but I'v had it for over a decade and I'm a very loyal person (it's never left me stranded). Suggestions anyone?