All of them go eventually. It is the rear self levelling.

You can get to the lines behind the rear seat, if you take them out and redo them. You would have to remove the rear seat. I saw it done. Be carefull or you will get fluid allover the garage floor. It is not too bad of a job.

Sometimes the accumulators/nitrogen cells, let go on them. Can happen at 50,000 or 100,000 miles. The "cannonballs" as they are called, can be replaced.

When they go out, the ride is VERY stiff and bouncy and unforgiving. You'll know.

In Europe, this system was optional on the 420SEC and 500SEC, standard on the 560SEC.

You could rip it out and install regular shocks, but generally, it is not worth it.

I would fix it. Or have it done.

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)