Gone in 60 minutes.. Cannot locate significant air loss

2014 KW T-680, Paccar MX-13, 585k miles.
Disconnected from trailer.

Turning to the experts on TTR for guidance on my air leak issue. Unfortunately the shop I paid $315 to today couldn’t find it.. Nor could the last two reputable shops I paid to find it when the leak was not as bad.

Started my truck this morning and noticed my air was depleted. Has had a slow leak somewhere that causes the compressor to kick on every 15 minutes..Two shops were unable to locate and I paid the bills and moved on.

This morning however, Compressor was kicking on every two minutes. Bring it to another shop down the road and they find a main air line push fitting leaking. They replaced that but it didn’t cure or even slow my air loss. Next they sprayed “everything” with soapy water. Unable to locate it I paid my bill and headed back to the truck stop.

Rate of air loss using the stopwatch on my phone.
From full charge until compressor kicks on 2.15 minutes consistently.
Full charge...shut down engine.
120psi to 60 in 12 minutes...50psi in 18 minutes.
Depleted @ zero in 60 minutes.

There are no audible air leaks. Primary and secondary gauge drop at same rate.

Starting to wonder if it could be a problem with or at the compressor (Seems the only place left to explore). Is there some kind of check valve at the compressor that could be bad?

I have another air related issue and perhaps perhaps they’re related..?

Over the last 5 months or so I have had 4 incidents where the compressor failed to kick on.
After the 3rd time I had the air governor replaced being that it was the cheapest repair to try. Two weeks later it happened again..

New governor kicks out at 120psi..the old one kicked out at 125+ psi.

Sitting in Enid, OK scratching my butt trying to figure out what to do.. Thinking to find a deep lake to submerge my truck in while I look for bubbles with a beer in hand

 

I just checked it with my bags dumped and the loss rate didn’t change..Had one replaced a couple months ago and I could hear it even though it was only a pinhole.
The mechanic today checked them twice with the soapy water.. Cab air bags soaped twice..also had one of those replaced along with a cab leveling valve.
Tried with brakes set and released..no difference. Even though the mechanic said it would be audible if the brake chambers were leaking he checked them with the soap water also..

 

Everything was done disconnected from my trailer..

 

From a little research I’m doing now I’m thinking that it could be a check valve at the air dryer...draining air back to the unloader valve..