Help, if you can...

My 2005 GXP wore out the inner edge of the rear tires in no time. I am seeing negative camber in the rear, but no significant sagging of the rear end.
Mechanic did find a DTC C0697, which points to the rear end leveling system. The rear air shocks are KYB's and seem fine.
The air compressor runs momentarily when I start the car and sounds good when activated by the inflation button in the trunk.
My concerns is if the load level sensor needs to be replaced or if the compressor isn't strong enough, or if the lines or shocks are leaking. I don't think it is simply a toe adjust that is going to resolve this. Lastly, my mechanic said that the rear substructure/subframe has significant rust/rot.

So my questions are;

Have others seen this and has anyone resolve it by replacing the height level sensor or other rear suspension or air parts?

Have others had and, or seen deterioration of the rear substructure cause it to be impossible resolve negative rear camber and, or toe-out?

All answers, insight and feedback is welcomed and gratefully appreciated as I have to decide if my Beloved 18 year-old Bonnie that I have owned and loved for the past 16 years is worth two new tires and any significant investment in rear suspension work...

Thanks.

If you have significant rot, you need to figure out exactly what is going on before moving forward with anything. The rear spring perches are likely rotted. What height is the rear wheel arch?

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

My spring perches are still good, but my wheel well and the right shock tower have rusted through at the bottom and at this point the shock tower is only attached by the top spot welds. Wondering if a shock mount bracket or reinforcement can be fabricated out of sheet steel, or if there is some way to lag rhe shock tower back down to the trunk floor panel.