The only way a modern car manufacturer can make their top luxury models to be so, is to have obviously high build quality, with current state of the art recognized exotic materials. That makes their products more costly to build, but that is OK, if you have a customer base to support this build quality policy. Mercedes in that era ad such a customer base.
To regain some of that reputation I think Mercedes could spend a lot more research and development funds to test car electronics to destruction in a much wider range of environments. That way their such top end luxury cars would bee seen much more reliable than they are now, with far fewer maintenance costs. The the customer base could see them as 'bullet proof', such luxury cars would retain much higher prices, as they age.
The dichotomy in this for any car maker however, is such cars when new would be so highly priced, as to be uncompetitive in the new car market, where profits have to be made.
The Lexus LS 400 is seen to be well engineered, ('bullet proof'), and was marketed at the time to compete with Mercedes in World markets. Today, the electronics of this car are still reasonably reliable. So is that rather nice 4 liter V8 engine, if it has been well serviced.
Mercedes had problems with wiring looms, and BMW had i Drive problems.