The air system leaks can drive a person crazy because there are so many places for leaks to occur. Some common ones are the regulator above the engine that controls the belt tensioner, the floor slide, and the air suspension system.
Prevost or the converter will be happy to find them. At $100 per hour anybody will be happy to try to find them. Often the easiest way to find them is patience and a logical plan.
One way to help is to be able to turn off each circuit individually so it can be determined which circuit(s) are leaking and making the effort to find the leaks easier. I added a shut off valve to each house air circuit. Now if I start puking air I can turn off the entire house air and narrow my search by 50%. No need to be this elaborate. A simple pipe plug will do the same thing.