I have a 1996 Royale Conversion and can't seem to find the source of my air leak. The rear of the coach dumps all of it's air over the course of sitting in my shop over night. I have replaced both rear air bags and the five (Norgren?) valves in the compartment under the driver's seat. Still have the problem.

The small on-board air compressor kicks on every three hours or so. Is there a check valve in the system to keep air from leaking back through the compressor?

My mechanic is stumped and so am I.

Thanks in advance for an advice you can provide.