Why install electical solenoids when you KNOW they will evenutally fail?

The fact of the matter is that vacuum systems to control things like HVAC air doors, emission equipment, and many other control functions throughout the vehicle are cheaper and lighter, and OEs don't build cars to last 15+ year without having to replace parts. In fact, all they really care about is that components last through the warranty period under worst case conditions. Believe me, I was an OEM production engineer early in my career, and they all have similar design and durability standards. Every other OEM has equally complex vacuum control systems as Mercedes.

You're probably not old enough to remember vacuum powered windshield wipers on the underpowered cars from the early post-war period. When you stepped on the thottle to accelerate, they stopped working!!!

Despite their complexity, cars are a lot better than 50 years ago - more complex for sure, but better and will last longer, but take increasing maintenance as they age. Same applies to airplanes, ships,... you name it. It always come down to whether it is cheaper in terms or time, expense, and risk of sudden failure and down time to keep fixing the old crock or sell it and buy a new crock.

Duke