There is much dismay to Mercedes' not covering the cost of repairing the evaporator problem in W140 (and other) chassis.
But, I'm amazed they covered ANY of them while the cars were beyond warranty. The same holds true for the 3.5L 6-pot diesel engines. Even with quality makes like Honda and Toyota, you'll be very lucky to have any out-or-warranty-period repair covered.
Now, you can make some argumene that these are "Mercedes-Benz" automobiles, and they should hold the bar higher. I think in many cases they do. Try any of the "Big Three" (from pre-merger days). Think you'd get any sympathy? Ha!
Think about the fact that even the problematic evaporators last years, sometimes a decade. How long do we expect MB to cover the car once the warranty runs out?
In my own experience, part of the problem comes in relatively low (compared to new) resale prices for S-Class cars. I know more than a few folks that stretched to buy a used W140, and then couldn't afford the repair bills. These were NEVER designed to be economical to operate. They are overly complex, leaden down with one feature after another, and often contain technology that has not been mass produced or debugged yet. That's why I own a simple C-Class. I don't want the headaches that come along with owning a flagship car. I owned a 911 Turbo, so I've my fair share of wallet-busting days.
The other problem I hear is low mileage vs. time. The other day I was at the dealer and there was a fellow with 1991 W126 560SEL hoping to have some repair covered. He was crying the blues because the car only had some 50,000 kilometers on it. "Why would it break already" he kept whining. Already? The car is nearly 13 years old! It's my experience that time wears just as bad if not worse than mileage.
Now that I've ranted, good luck on the evaporator repair if it required.
1998 C230 "Black Betty"