If you still have the owners manual for the car, you should check what it says. They typically specific precisely the BOSCH spark plug required. If you don't have an owners manual, you can ask other folks on the board and also cross-check with the Chilton's manual which is USUALLY but not always correct. Don't put the champion equivalent in there, etc. Also, only use the original copper spark plug, do not put platinums in there-- those have been known to cause issues. And finally, the correct plug wires need to be in the car-- use only the Mercedes/Bosch plug wires, they are built much better and have the correct resistance for the plugs that are in the car. On my 380 SL, there is resistance built into the spark plug wires, that's why the plugs have no resistance in them.