At 55,000 miles (after warranty expired of course), my GL started to exhibit the usual signs of airmatic failure. After parking over night, the front end would sink until there was no space in between the fender and tire. This would happen intermittently at first. The frequency started to slowly increase and eventually, it would sink every time it was parked. Time to change the POS shocks. Online, they went for around $1000 a side but through the power of this forum, I discovered Air Suspension Kits, Air Shocks, Suspension Parts, Struts - Arnott Industries
and was able to buy the refurnished ones much cheaper. I had a minor issue with the order and arnott promptly took care of the problem. I wrote an email to them Christmas eve not expecting a response until after the holidays but I received a reply that day stating that they would take care of the issue. Unbelievable customer service. I highly recommend them and will order the rears from them when, not if they go out.
On to the procedure.
1. Loosen the lug nuts on the side you’re working on and jack up the car at the jacking point. After the car is jacked up and on stands, remove the lug nuts and remove the wheel.
2. Remove the air hose from the top of the shock. Loosen it slowly and once you hear hissing, stop and let it depressurized fully. Then remove it. You can tape the end to prevent debris from going into the line.
3. I went ahead and removed the strut bar. It may not be necessary but it was quick to remove and gave me a ton more room to work around. Remove this box first and the strut bar came out with 4 bolts and a 10mm on top.
4. Break the tie that holds the brake line on the strut. You cannot salvage this as it will be very brittle. Mine on one side was already broken. Remember to get some replacement ties and re-tie them back on during installation. Once it is broken, you can rotate the brakes lines out of the way.
5. Remove the lower shock-mounting bolt. If you have an air gun, it will make the job a lot easier. If not, I hope you have a big breaker bar.
6. Remove the link nut. These things are notorious for spinning and not loosening. Again, if you have an air gun, it will come right off. If you do not have an air gun, you can use a torx bit to hold the bolt in place and use and open-end wrench to undo the nut. Example below.
7. Remove the upper control arm nut. Same issue as above.
8. Use ball joint separator to separate the control arm and the link. Use the proper one below and not the one that looks like a tuning fork.
9. Remove the three nuts from the top and you should be able push down on the lower control arm and slide the shock out.
10. Installation is the reverse.
I would also recommend getting an alignment done as the front end might be tweaked from this procedure. There was no difference in ride quality that I can discern from the original and rebuilt shock. Overall, the job was fairly easy, especially since I had access to an air gun but it is quite doable without one.