According to the service manager at my local M.B. dealer, the self levelling rear shocks do not need to be replaced in pairs as regular shocks do when only one fails.
By the way Joe: I strongly disagree with you, in my opinion "IF IT LEAKS, IT'S BRITISH" (just ask any Jaguar or Land Rover owner).
CL 500, 1998
S 500 L, 1998
E 320 T, 1995