The cabriolet's hydraulic top rams, switches, and lines are the single biggest cost/risk item; leaks are considered inevitable, and the consensus is to replace the entire set at once rather than chase individual leakers ('finger in the dike'). A full OEM/dealer job has run around $12k, while Top Hydraulics rebuilds are the widely recommended cheaper alternative; a car with the work already done is treated as a major plus.
A124 convertible top hydraulics: the all-or-nothing job
Mercedes-Benz W124 E-Class · mechanical