Welcome back my friends to the show that never ends...I'm so glad you could attend, come inside, come inside! (Apologies to Emerson, Lake, and Palmer)
Difficulty level: 4 out of 10
Frustration level: 8 out of 10

Passenger side rear air spring developed a leak. Losing ~1 Bar pressure every five minutes confirmed multiple times with Xentry/DAS.
A few tips for others doing this work:
-Drop the rear toe arm to provide room to remove the air spring (my toe arms are aftermarket)



-Release spring pressure using Xentry/DAS. Will drop to ~3 Bar and then you will need to crack the air lines to release all pressure.
-Remove bottom bolt and use a pry bar to remove air spring.
-New air spring would not(!) fit into the aluminum air spring control arm. It is shaped like a "V" and the middle was just too narrow to fit the bottom mount of the air spring. I ended up loosening the inboard bushing bolt on the sub-frame and using a pry bar to spread the air spring control arm enough so the air spring bottom mount would slide (sort of) into place. It still required a long narrow punch to wiggle the mount to align with the control arm holes. I then literally threaded the air spring bolt into and through the control arm. Ensure the top of the air spring is securely fastened to the stud attached to the body! If not, the air spring will fail within weeks or months!
-Inflate air spring to ~0.5 Bar. Use a floor jack to lift the outer hub. Lift the hub until an inclinometer (download the app to your cell phone) laid on the drive axle measures -1.2* inclination angle (hub higher than the differential).
-Inflate air spring to ~2 Bar. Verify the air spring is not kicked out in any direction; front/rear, left/right. Tighten lower air spring bolt to 150 N-m. If you had to loosen the inboard bushing bolt as I did, tighten to 50 N-m plus 90* or ~85-90 N-m.
-Lower the control arm and remove floor jack. Inflate air spring to 5 Bar.

If all is good, now is the time to reinstall the wheels, lower the car to the ground, start car, allow suspension to fully inflate. You can then raise/lower car 2-3 times and then re-calibrate the Airmatic suspension ride height which will take you an hour or so the first time. Once you have the inclination angles associated with ride height, in the future, you can just calibrate to the proper ride height and enter the previously determined inclination angles and press "save". This might take you a half-hour or so.

For me, all was not good. Went to reinstall the wheel and one lug bolt would not start. After several frustrating attempts to start the bolt, I realized the lug bolt had broken off in the hub...
Great.
Best case, easy to remove. Worst case, pull the hub.

I did not remove the brake disc (too many other complications for me to want to do that). The fracture was angled at ~30* to 40* so that would make it difficult to start a drill bit into the center of the broken bolt. I used a "pyramid" tip punch and a hammer to make a small divot (or small sharp depression) in the center of the broken bolt. I then used a very small left-hand drill bit to enlarge and deepen that depression. As the depression enlarged, I would step up the next larger left-hand drill bit. Lather, rinse, repeat. I worked up through the next five drill bits with the intent to finally drill all the way through the broken bolt and use an extraction bit to remove the stuck piece. Slow and steady and I lucked out...

Left-hand drill bit for the win!



If you don't have one of these, you should.



At this point, I no longer trust the remaining lug bolts that came with my aftermarket wheels so I am replacing all of the lug bolts. I went with Acer Racing's titanium lug bolts:
https://www.acerracing.com/products/...8mm-38mm-shank
I would not pay $700 for a set of titanium lug bolts but when "on sale" for $230, I'm on it.

I'll post next on how to determine if you have a leak in just one air spring or the inter-connecting system that ties all of the air springs/struts/reservoir together.