i spoke with the mechanic who did the 10k maintenance. he put a 18mm plug so that leaves even less clearance around the plug. he told me to bring a 18mm deep socket (from the hardware store) and he will machine it for me. i had bought the Cruztools 5/8 16mm spark plug socket thinking the plug was a 16. That one should work for the 16mm plugs as its outer diameter is about 20-21 mm.