Cab airbags deflating after shutdown

Hi friends. My cab airbags deflate after shutdown even with plenty of air in the system. I’ve checked for leaks with my handy squirt bottle of soapy leak detector and I don’t see any leaks nor do I hear any. Then for some strange reason it just drops like I punctured one of the bags. Is there a separate check valve or is there a check valve built into the leveling valve? Thanks

 

2003 379 daycab

 

I’ll have to follow the air lines to see where they come from. I’ve sprayed the valve and the air bags many times and can’t see a leak anywhere. Then all of a sudden it will drop. And when it does you can’t hear any air leaking. I had an airline leak. The 5/8 line from the foot valve to the back of the cab and the next morning the cab was down without a load on. This morning the cab was up with a load on. Very frustrating.