Land Rover Repair: Discovery 1999 TD5 back suspension drops, soleniod, best bet

Question
I have a discovery TD5 1999 whose back suspension drops when the car is stationary in some circumstances. The suspension rises ok when you start the car. The circumstances when it drops are: 1) leave the car parked on a hill, rear end down the hill 2) stand on the tail gate or load the car with more than the usual weight. I took it to a LR dealer who tested the air bags and told me that they were not leaking and would need the car for longer for further investigations. Considering their extortionate hourly rate and their previous inability to diagnose a problem, I am reluctant to pursue this until we have more information from other LR owners. Some ideas we have so far are Soleniod or relay problems in the self levelling that occurs when the engine is off. Any advise would be appreciated.

Answer
There is no home diagnosis of the air suspension.  Your two options are to trust in the dealer's ability to fix it, or buy a kit to convert to coil springs.  Coil spring conversion is less expensive than most repairs, so unless you really want air suspension for some reason coils may be your best bet.