The rear plugs were fouled with burnt carbon after about 500 miles, one of which stopped firing (which caused me to pull them).
Oil was also on the threads below the sealing surface on three of the four rear plugs. Once changed, I got another 700 miles or so before the same condition occured.
Oil consumption is not as bad as when engine was new. I'm thinking plug gap will affect either burning the
oil off the plugs before the plug finally fouls with carbon. My initial plug gap was .045 (should they be .050?). I saved the plugs but I didn't number them. I can probably identify the two or three culprits and post a photo tomorrow.