Hi.
What is the suggested procedure to find the leak ? Spraying soapy water ?
Any locations prone to cause the problem that deserve more attention ?
Compressor kicks in OK after closing the door and restores height with no problem.

 

check folds in bags and connections really well. soapy water is the way.

 

Like dusty said, spray then with soapy water and look for bubbles.

Here is a great write up on the SLS:
Disco 2 Disco II Air suspension – the definitive guide! - Land Rover Zone