The W140 chassis is an awesome automobile but not without it's warts. I can only fairly comment on the 500SEL as I don't have ownership experience with any other configurations. It has been said that the W140 (particularly the 500 and 600 SELs) is the last of the big Benz's, and that is probably true. The size and weight don't even compare with the newer S class cars. Mileage is most certainly not a selling point when talking about a 5 or 6 liter V-8 or V-12 pushing a 5500-5800 pound vehicle.....but I doubt gas mileage was a real concern when designing the ultimate automobile in the late 1980's. The series has a whole lot of electronic goodies that are failure points on these cars and they aren't cheap to repair. Most are not items considered "necessary" and if they fail just don't fix them....such as reclining rear seat, remote locking, door closing assist (except the trunk won't close tightly!), etc. Mechanically they are Benz's, well-engineered and bullet proof if well maintained, but costly to repair. They are probably one of the safest vehicles to drive, so that is something to consider as well As far as insurance goes, I have found that it is very reasonable when these cars get to 10 years or older. All considered, owning one of the finest automobiles ever made for a small fraction of original cost is a strong selling point....but you must have some 'risk tolerence" when it comes to upkeep and repair.

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold