The consensus maintenance budget for a driven car is roughly $5k a year (some owners say $2-3k for a lightly used one), reflecting the sheer number of complex luxury systems. The repeated theme is that a properly serviced 140 is trouble-free while a neglected one is a nightmare, and that deferred maintenance, not fragility, is what bankrupts owners.
Running costs: budget several thousand a year, and sort it or suffer
Mercedes-Benz S-Class Coupe / CL (C140) · ownership