^^The previous owner (my father-in-law) bought the car new and was very careful about having all needed maintenance done. None of the things that have failed so far would seem to be affected by doing or not doing the proper maintenance anyway. The car is a lemon, plain and simple. W220s are known to be problematic, and we seem to have gotten one of the more problematic ones.
Don't think you have mentioned what other issues you have had on the car?
We have had 2 different fuel system parts fail, and the previous owner had a big file of repairs: one of the airmatic struts repaired, the battery and a bunch of charging system parts replaced, a few other things.
A 2003 Subaru would probably have had some issues too, even if perhaps less than a typical W220.
As it happens, my 2003 Subaru WRX has 50,000 miles on it (vs 30,000 for the S500) and has had exactly $0 cost to me for nonroutine work. It has had 2 CELs--both checked and cleared under warranty--, warped brake rotors replaced under warranty, and what I thought might be a wheel bearing noise checked and determined to be just noisy tires. The last item was not under warranty and not the original tires, but the dealer still did not charge me for the 30+ minutes various techs spent listening to it and checking the bearings.
Referring to another recent thread, I don't think it was completely fair to charge you the full diagnostic time, benzofreak might have done it in a quarter of an hour.
Good point but I doubt there is much I can do about it except never go back.