Hard to Finding small air leaks

After 6 yrs of chasing air leaks, I am down to the hard-to-find ones on the following items & have replaced all of the following over time. The leaks were very small and difficult to detect. I am at the point where my brake tanks stay up for weeks and my Aux tank drops down to 60 PSI overnight and then slowly down to zero over the following week.
I have accepted the leaks will never get to zero and if I do get them to zero it won’t last for long.
* End caps on Norgren valves
* Pressure regulators for engine belts and generator air bags
* On/off valve for engine belt air bags
* Drain valves on tanks
* Pressure relief valve on air dryer
* Pressure regulator line to engine air compressor governor
* Air valve for steering wheel adjustment
* Parking brake valve by driver's seat
* Connectors on back of front & rear brake tank dash gauges and Aux tank dash gauges
* Quick connections for external portable air hose. The female connector leaks internally at the O ring and is hard to detect.

Hope this helps
Chuck

P.S. And there's also the interior pocket doors and entry step cover air cylinders.

I put a quarter turn shut off valve on the QD connects for that very reason.