[folivier]

On my '98 I had a persistent air leak that I finally figured out. After addressing all of the obvious areas, generator slideout valve, air ride seats, etc. while crawling in one of my basements I looked up and found a length of 1/4" tubing coiled up and tucked up. The end of it had a collar and plug. The plug was just finger tight with no sealant on the threads and yes it was leaking air. Pulled the plug, taped it up, and cut compressor time considerably. Not sure what that tubing was for.
Look around there may be something like that for an unused item.