2003 GMC Envoy Air leaking out of rear air leveler springs

Suspension problem
2003 GMC Envoy

I have an 03 Envoy XL. Same as a Trailblazer Ext.

After the car sits parked for a few hours the right side sinks down and in time the whole rear sinks. Most of the time, not all.

I start the car and the compressor seems to be running great, and it pumps it up just fine. Perfect.

I don't think this is normal and I read some threads about similar problems, but no one has said where the problem turned out to be though some have replaced their air leveler with ordinary springs. That seems precipitous to me at this point.

I suspect an air leak in the right air spring or maybe it's associated tubings and fittings. And after some time it leaks from the other side, perhaps across the system or through the pump and solenoid valves and out the leak in the right hand side.

The leak might be in the air springs, with are about $130 each for the GM parts plus shipping (online price) or about $180 for a pair of aftermarket air springs made by Arnott.

The leak might be in the air tube of which their are two at about $10 each.

Or there is a check valve for the compressor for which there is a GM rebuild kit for about $26.

It could be a leak in any of those places. Does anyone have any comments, where I should look first?

Can anyone comment on the Arnott aftermarket air spring product, compared to the GM OEM air spring product (Incidentally, I found out those are made by Firestone Industrial for GM).

Can someone suggest another place the leak might be, or is there another cause of this symptom that I should be looking at?

Thanks in advance for any help. I haven't had this car long so I am not all that familiar with it. I have to resolve this.