Gary,
We have the same year and model as done by Liberty. When we got the coach, the aux ran much as hers does. We had to do all the time consuming chase down of lines as Ken mentions.
Our big leaker, it turned out, was the check valve right after the compressor. It would allow air to escape back through the aux cylinder head to atmoshere. Easy to check by removing the air intake filter and placing your finger tip over the intake. Releasing after a couple of seconds made a popping sound.
There are plenty of other places to look but this is an easy one and cheap to fix.