The plugs were changed in regards to the TSB about 12K miles ago. I threw a CEL and it came up as misfire on cylinders 3 & 4. Did a compression check, and the compression is fine. New plugs going in. Either Densos or NGK iridiums at a degree cooler. With the S/C, you can see where it was leaking out onto the porcelain part of the plug.

 

That "leaking" is normal and most who inspect plugs find similar results.

 

I'm not so sure it's "leaking". Almost all S2000 plugs will look like this in time, both NA and S/Cd. I think it is due to the high heat in that area where the metal part wraps around the ceramic part. The upper portion of the ceramic doesn't get the heat transfer quite as badly.
Looking at the gap on the second plug, it looks kinda big. For your application, did you narrow the gap down to the recommended 0.032" or so? If it was at the same gap as for NA, over time, it may have been this that threw the CEL.