I am preparing for my 60,000 mile service(which I will do myself) on my 06, and I am finding a conflict on which spark plug to use. My Subaru maintenance manual says NGK ILFR6B. If you go to the NGK(or sparkplugs.com or Amazon.com) site, they say to use NGK ILFR6T11, and the ILFR6B is not for the Tribeca. I can't find any real difference between the plugs except the price(the ILFR6T11 is usually 50% cheaper). They are both the same size, are mid heat range and are iridium. I assume it currently has the ILFR6B in it now but I don't know for sure. Sometimes after a car is out for a while a better plug is available. Any comments?