Im currently rebuilding my shock absorbers on my 2005 E500 4-matic Airmatic. 211.083
First I want to point out that I know there is plenty of options on getting new or rebuilt shocks but low price often reflect in quality and most cheap alternativs don't use the ADS function.
So my solution is to rebuild the front shocks for myself not only because of the price of new ones but as a prof of concept that it can be done if you have the right tools.
i have fully equippd workshop for fabricating most parts and tools so I take it one step at the time.

Dissasambly is not that hard and changing oil in them is fairly straightforward.
Nitrogen chamber needs a service port installed I use 1/4" ac connections since this works well with my nitrogen charging bottle.
when emptying old oil I pressurize the chamber to get the piston all the way in getting most part off old oil out.
then for filling I use Vakuum to pull piston back and also to check for leaks.
The top seal is a bit tricky to change and needs som fabricating to be made I will go into this later but for now I start with the easy steps to se if I get it to work.

But som question have arised along the way.

What oil wold be prefferd as an oe replacement "not brand specific" just looking for 20 CST @40deg or 5W Syntetic or mineral etc I live in Scandinavia so products commonly found in US can be hard to get her. Motorcycle fork oil is easy to obtain but not really sure it is good for this application or is it better?

Second what wold be a good pretension pressure in the accumulator anyone know or have a formula to calculate pressure ?
My test shows that minimum seems to be 75psi. and at 300psi it feels like a "new shock out of the box" but im afraid this might be a bit to much

 

Top seal was leaking its a 2 o-ring and seal ring design. I think this solution is cheap to produce and will be good for the oe specified service life.
I decided to take a different approach using parts I can source local.
hopefully it will last as long as the oe solution.
i will put radial seal on outside just as dust protection maybe I can finde a little smaller solution but this was on the shelf and under the blue seal I will use ptfe bussing like the oe solution.
but bussing will be a little different design.
some machining to do to the top end but not done yet since threading in my old lathe is quite hard I'm waiting for som help from a friend with this.

I found 2 oils I will start to try one mineral base 25cst @40deg and one synthetic 20cst @40deg
to what I think I found oe use mineral base but not confirmed. so this need som RnD

 

Final design probably the top radial seal is not needed since it is inside the the air strut but not much extra work to make it so better safe than sorry.