Your suspension has ride height control valves that adjust the bag pressure on the fly to keep the suspension at the correct height. It's basically a lever from the chassis to a valve at each bag. Some of the bags may have their own ride height valves, while others share one lever control through a common air line. There will also be an air feed into each bag, and somewhere a dump valve for releasing all pressure in all bags. Any of those valves or the associated fittings could develop a leak but they are industry standard parts and should be easily replaceable. Most truck suspension shops should be able to provide the part.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL