hello,
I had the same problem as you with my CLK 430 but I have 16 plugs......
I just can tell you that I had BOSCH platinum F8DPP332 and I replaced them With NGK IFR5D10 the same for your engine.
Thise plugs are Ok and engine run perfectly.
I used a 17 mm open wremch also to remove boots.
Take your time to remnove the old one..........4h for me to chenge 16 plugs...
I hope will help you
Alberto