Installing front hydraulic SLS suspension on the W124 S124 is a modification that i have not seen before.
The W124 is not factory availible. This was optional on the R129 and W201. The W201 system is pretty rare and to rare to use this parts. So in my install i using R129 parts. If the are availible. i have used oem R129 hydraulic shock absorbers. These are still new availible from the dealer
The hydraulic valves for control of the firmness or sport setting is to rare or to expensive to use. So im using industrial parts to controll this. If these parts fail in the future then the are easy to get and to change out. The level valve im using a OEM part. For controlling the level outside of the weight load adjustment. Im using aftermarket parts.
I have installed the system for the firmness adjustment on both front side of the car, These systems are installed on each side in the wheel arch. the firmness adjustment will have 2 base settings. comfort and sport. The base settings can be set with 2 valves that can reduce the flow of oil to and from the shock absorber to the spring accumulator.
If there are any questions just ask