Hello, I have inherited a 2012 CLS 550 Base model and could really use some input regarding issues with its suspension and the repairs it has had. If this is not the internet space to ask or if there are other resources that you think will help me I would appreciate any alternatives. I am pretty slow with mechanical engineering and automobiles though I am doing my best with internet sleuthing.

Okay here's the story:

My friend has noticed that both sides of the rear suspension has been getting lower. He has taken measurements over a number of days with the battery disconnected and it is indeed getting lower. My mother has had these issues for a while but has spent a lot of money getting it repaired over and over.

-November 27, 2018
-Airmatic Suspension Fault comes on and car leans to right.
-Dealer 1 runs test
-Compressor test ok
-Can hear Airmatic line leaking.
-Locate leak under battery
-Found line chaffed on battery box
-Cut out damaged area of line and installed repair line
-Replaced Connector (000-327-01-69)

-October 16, 2019
-Dealer 1
-Suspension is lower on right side.
-Replace Right Front Strut (218-320-66-13-80)
-Replaces Auxillary Battery (000000-004039)
-*Websites say this auxillary battery does not fit 2012 CLS 550

-October 21, 2019
-Dealer 1
-Right side suspension is down.
-"Repair Vacuum Line"
-"Repair Vacuum Line To RF Strut Leaking"
-No charge

-January 04, 2022
-Dealer 2
-Right side suspension will not raise
-"Right front and right rear air springs blown out."
-"Airmatic compressor very weak."
-Replaced Right Rear Air Spring (212-320-40-25)
-*Website says this is "without sports suspension"
-Replaced Airmatic Compressor (213-320-04-04-80)
-Valve Block (212-320-03-58)
-*Website says this valve unit does not fit 2012 CLS 550
-Did they charge me $515.00 extra for no reason?
-Relay (000-982-85-23)
-Valve Unit (212-320-06-58)
-Replaced Right Front Airmatic Strut (218-320-66-13-80)
-Special ordered 2x Connector (000-327-01-69) @67.00 each

My friend thinks I need new rear air springs and will help me replace them. I trust him and want to order the parts. My questions are:
-What else do I need to purchase? I want to be sure to everything I need so as not to waste his time.
-Based on the above invoices there have been line leak issues. Should I be replacing all of those too? I do not want to continue replacing parts when they are simply failing due to another reason.
-Why did Dealer 2 buy part valve unit 212-320-03-58 when it does not fit my car? They also bought another valve unit 212-320-06-58
-Dealer 2 replaced Right Rear Air Spring with (212-320-40-25) which the description says is "without sports suspension"
-I checked and indeed I do not measure a height difference in rear of car when switching between Comfort and Sport
-If I replace Rear Air Springs should I use "with sport suspension" parts 212-320-44-25 and 212-320-43-25-64

I would hate to find out my mother has been getting ripped off or anything like that. Two different dealers replaced the right front strut within a couple years. After Dealer 1 replaced the right front strut, the car's suspension went down again 5 days later and they repaired a line leak in the right front strut.

Any help or direction would be appreciated, and thanks for reading if you've made it this far.