Hydraulic power windows?? In doors? Man, I had enough trouble bleeding a hydraulic clutch properly, and that line was maybe 30 inches tops.
And hydraulic power back seats, and a hydraulic sun roof (!!) and hydraulic power aerial, and hydraulic controls for the air suspension. Some models even had a hydraulic glass partition between driver and passengers. Absolute nuts. But the high point of dead-silent, powerful, smooth conveniences no matter the maintenance cost.
Wife's car broke down (probably the water pump or just a loose hose) on the highway while coming back from vacation. As it was a very busy day where we were (France), there were not any regular cab left so the insurance company sent us a driver with... a Mercedes S class 550 (not a taxi but a private driver: no "cab / taxi" thinggy on the roof). It's still as you wrote: dead-silent, powerful and silky smooth.
Diesel engine but as a passenger I honestly couldn't tell, even though I'm a petrolhead and tend to notice these things.