2001 Jaguar XK8 - Replacing Spark Plugs - Tons of useful information 

Great video, especially the tips on anti-seize coating on NGK plugs as well as the specifications for Iridium. Here's the kicker: owning both a 2001 XK8 and a supercharged 2001 XKR, I changed the XKR spark plugs last weekend and was astonished to find NGK PRF5G-11E (Laser Platinum) items that appear to have been there from the factory. Gaps far exceeded the .043" tolerance at 52k miles. Oil had leaked into some of the ignition coils that required a bit of cleanup. You may have discovered that your engine has also been harboring some older standard plugs or perhaps the tolerances were beyond spec.