Save the trouble and the cash, and install Bosch Platinum at $2.17 per plug, or Bosch Platinum+4 at $6 each. The Bosch work just as well. Unless your originals are so fouled up, or the resistor has been degraded due to an over-extended interval of service (over 60k miles), you will not see any performance or mileage gains.
I believe the plugs you can use are Bosch Platinum 4202, and Platinum+4 4418. Check the www.boschusa.com website to be sure. I have the Platinum +4, but if I were to do it again, I'd go with regular platinum and save the cash. They are quite easy to replace by yourself as a DIY, it takes about 45 mins.
I know you guys are going to croak when I tell you this but... I replaced my original plugs at 90k in my 97 S500 with standard everyday-even boring Autolite plugs from my local auto parts store. Gas milage increased (about 1mpg) and car runs better. The electrodes in the old plugs were worn out and the resulting gap was almost twice the spec. Total outlay- about $9.00.
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