On my 2008 SC, I replaced both front struts 2 years ago due to a leak, All was well. The rear airbags started slowly leaking down after a week of sitting. All of a sudden the entire rear would drop to the bump stops over night( it was at the paint shop for 5 months so during this time it this started happening). I replaced both rear bags and there is something else going on. The rear of the truck drops evenly not one side. I have leak checked everything i can find and can find no leaks.
I think there is an internal leak in the rear valve block. I took the compressor cover off and leak tested that also.
But there is also another problem. The truck will slowly sag a couple inches over night but the air compressor is cycling every 2 mins or so with no drop in the vehicle height. If there is a slow leak it would not explain how quick the air compressor is cycling.
If the valve block at the compressor is leaking back through the compressor and the rear valve block is leaking back to the main gallery would this not describe the problem?