Hi
I have just replaced a front airbag on my 2000 Range Rove p38 yet as so as the engine is off the front off side drops. It does reflate when the car restarts but assume the loss shouldn't happen. We have cleaned the valves but to no effect.

Any thoughts?

You obviously have an air leak. There are only so many places that can happen, check them. The bag. The connection to the bag. The pipe. The connection of the pipe to the valve block. The small O ring in that corners valve base. The seal on the solenoid valve shaft. If it's not leaking from one of those places you are imagining it.