O2 Sensor problems of the 2002 Mercedes Benz S600

While driving vehicle suddenly car began to lose all power, check engine light came on, car began running rough. Took to dealership and they reported that the oxygen sensor was faulty and both right and left coil packs and that they need to replace the spark plugs again, at a total cost of $3875. 00 this seems very disturbing considering they already replaced the spark plugs and wires because they were defective parts from the factory under warranty but now refuse to take resposibility for the coil packs even though they admit there is an issue with these high ignition systems. Only 14275 miles on vehicle.