 Bought the 2010 S550 4-matic with every option as a lease return CPO at almost 1/2 the original purchase price at two years old and with 20K miles on the ode.  Bought an extra 2 year warranty and have only had to use it once for the drivers wheel sensor.  Dealership replaced all the wheel sensors just to make sure.  Oil, brakes, windshield wipers, air filters and one set of tires is all I've put into this car with over 60K miles of almost daily use.  Tires made a huge difference - bought Conti DWS and that made this car perfect in all weather and super quiet, including managing a foot of snow on the road.  I've had no issues with transmission or engine - starts off the line fast in sport mode, rides smooth in comfort, shifts great with no hesitation between gears.  I've owned over fifty cars (all types) and this car is one of the best.  I'm 6'6" and the drivers seat fits perfect - If I want, I can put the seat back far enough so I can't reach the pedals.  Massage, heated/cooled and fine leather seats are perfect for long trips.  Oil changes at the dealer (MB-PDX) with a free loaner (due to the car being S-Class) has been great.  60K highway / freeway miles has averaged 20 mpg (per the panel).  Finally, I can sell / trade the car for about 1/2 of what I paid which isn't too bad for driving this level of comfort.