Wifey's 2007 Mountaineer developed a intermittent miss with no check engine light. Pulled a coil pack and the plug boot looked like this.
I pulled all the coil pack/plug boots and squirted in some dielectric grease (available at auto parts stores). Reinstalled and the miss was cured. I just wonder how many coil packs have been replaced all because of a little continuity or ozone buildup problem? haha