I had had 2 air leaks, one at the compressor, and the other at the T for the front bags. The one at the compressor I could hear, so I knew where to spray some soapy water, the other I had no idea and had to do it the old fashion way -> crawl underneath with a spray bottle (Soap and water mix) and start spraying. I did mine with the engine off, but had an assistant. The assistant's job is to watch the air guages, when they went to 70, come out and tell me. I would then crawl out, they would start it, build air back up, shut it down, and I would start spraying again. Finally heard a slight hiss when I made my way up front and was almost near the center of the rig, just behind the axle. I sprayed and found it. It is tedious, should not take more than a few hours. If you know someone with a pit, or a lift, it would probably go faster and be much easier. Don't forget to block it before you crawl underneath, mine has air suspension so any leak and the bags will deflate, and even with the jacks down I still did not trust it.
2007 Fleetwood Excursion 40E Cat C7 350 HP
2007 Chev 2500HD D/A Long bed CC (Yes, it is my TOAD :B)
2011 Toyota Tundra
2013 Jeep Wrangler Unlimited Sahara (Backup towed)
Gone but not forgotten, 2008 Jayco 299 RLS