This is a very random issue with my Discovery 2. Randomly it lets the air out of the left rear bag. Any ideas?

 

Bad height switch, I bet.

 

I figured that or a valve block. I did find a leak in the bag after I posted this. but only if the suspension is past a certain point in the travel....

 

http://www.arnottindustries.com/is having a sale on their lifetime guaranteed air bags at $129 a piece, sounds like you will be needing some soon.
I also know of some one that is removing the SLS from his 03 if you are interested in buying some pretty low mileage SLS parts.