Hello. I figured out what was the source of air leak in driver side airspring:

The picture above is with all wheels on the ground
The picture below is with all 4 wheels off the ground:


I think I am getting out with just a scare: I need to replace O-ring in the valve
Does anybody knows size of O-ring used? Any recommendations?
I found few on e-bay:
https://www.ebay.com/itm/13509222206...tion=view_item
https://www.ebay.com/itm/37302396175...RG20Z18SDNVKEF
For the low price it may be not worthwhile messing with O-rings; however that valve saves some air in the shock when system fails.
The better question is where to get a spanner wrench to get those valves out?!
Thanks in advance!

 

I found this tool with help from "Miessler Automotive":
Yes, it is European Amazon.
This is also available at US Amazon site:
See the price difference?
Ordered from German site! $37.92 delivered to my door!
I can wait.
I decided not to go with modifying 14mm deep socket. This can be an option if wait is an issue.

 

Jack the leaky side up to normal height, before removing valve. Should stop damage to the bladder when the valve's safety pressure is released.

 

But of course!
The question though is:
After replacing valve, there is no pressure in the air spring. The only way I can make air go into the air spring is SDD, isn't it? The jack should not be lowered, untill pressure in air spring has been built up. System will not let air in untill sensor shows the corner is low.
Is my logic correct?

 

Look up Miessler Automotive (Germany) they have them new . Pressure Retention valve , brass connectors , nylon hoses 6 and 4mm, couplers , repair kits and all the necessary seals as well as new rear height sensors with bracket

 

@Petz Thank you, I know Miessler, I was thinking about those lines: make an adapter for compressor to blow into airspring. all it takes half a meter clear pneumatic hose, pneumatic coupler and a blow nozzle.

 

Can recommend Miessler as well. Their Electronic Damper Shocks for BMW X4 worked perfectly and were a half the cost. They have similar shocks for our X350s but I since everyone goes Arnott I am going to go with the proven part on those.

 

You could try this Aliexpress

 

Some had trouble with the Miessler airstruts I know of two cases. One personally. They took em back and reemboursed .That was 3 years ago

 

That was on x350 xj8

 

Reporting some progress:
1. That tool I purchased on AMAZON:
OD is too large; teeth are too big. Good thing I did not buy it on US side it was 3x more expensive. Oh, well, live and learn!
I just grabbed hex bar stock of free machining steel in machine shop and made one. It took me about 30 min turn and mill it and then coming back to turn OD down 0.25mm.
Commuting from home to work 2x times took more time than making it!
Any way I am attaching drawing for this wrench if someone wants to make one themselves
Here are pictures of this tool:


Naturally, I jacked up the wheel I was working on to reduce forces on air shock.
After cutting down 'used' portion of air tube approximately 6-8mm lubricating O-rings and threads with lithium grease and installing new valve. I did following: I used similar sized pneumatic tube, connected one end to valve, and and shoved compressors airblow nozzle into another end and held it together for about 5 minutes. The only leak I heard was leak in quick disconnect.
Disconnected rigged line.
connected line from car, lowered jack to approximately correct height. Car was still supported by jack.
Started car let run for a while. air compressor is very quiet and changes in coming from worming up engine muffled compressor noise.
Any way three minutes later I decided to test my luck and lowered jack completely.
Car did not sag a bit!
wheel arch apex to center of the wheel 'measured' with tape ~380mm one side ~390mm the other side.
No bubble at the valve!
Took car out for a short ride; came back measured height again, everything as it was!
Car is playing garage queen in winter months so I will see and report in two weeks.
So far it is looking good!
Thanks everyone for suggestions and moral help.

 

I will call it FIXED!
Over two weeks in single digit weather. Car is not driven since repair was made. Car is on trickle charge.
Have not dropped at all.
Next step, when weather above freezing, I will be doing rear suspension arms.