rkalos - I had a similiar situation with my Range Rover.
As it turned out, the rolling of the air bag during driving creates a fatigue spot in the rubber, (mine dry cracked in the center)
If it wasn't loaded, it might leak down overnite, but with a load of cargo, or while driving, it would stay inflated for days.
I replaced the bags with arnott air bags and new oring seals and didn't have any issues for the 2 yrs. I kept it.
Spraying the whole system down with soap bubles will find your leak(*)