All U.S. W140 S 500s have rear axle self-levelling suspension as standard. This system was only standard worldwide on the S 600 and an option on ALL models (from S 280 up to S 500).

All W140s (S 280 up to S 600) had the option of A.D.S. This system is hydroneumatic (not air) but more sophisticated than the more mundane rear self-levelling setup. A.D.S. acts on BOTH axles front AND rear and is very easy to check if you have it by a suspension switch on the left or right side of the central dash ashtray. No suspension switch - no A.D.S.

The rear self levelling suspension system on the S-class is very similar to the setup on the E-class wagons. As stated correctly by JimF, the spheres are the first ones to go. They will fail either by age or if someone has driven fast once or several times over speed bumps. The sphere has an interior membrane that is very susceptible to harsh bumps, hitting hard the suspension over speed bumps deteriorates this membrane faster or it can even brake suddenly.

Due to the obvious weight, front regular shocks are also prone to sudden failure when the car is also abused at speed bumps or a deteriorated road. 100k miles might be a good general road rule for regular M.B.s, but S-class shocks deteriorate on ride quality much faster than that.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]