2x on checking fittings!
We had a RR air issue - slow to raise and didn't raise one time. Intermittent issue - not always happened. I was thinking air compressor.
Was doing engine work (thermostats/hoses/belts) and was cleaning off road grease and gunk underneath. Had a Schrader valve and piping "fall off in my hand" while wiping it off.
It was "T"ed into the air suspension piping right at the air pressure/filter setup. Wasn't sure what it was until I cleaned it off and searched the number on the fitting. (it was black and non-descript when it fell off in my hand). Turned out to be an air check valve. I made sure everything was working and reinstalled, snugly.
Air issues went away. Suspension pumped up quicker than before.
The "valve" after cleaning.
Reinstalled in piping.