spark plug blow out

Hi all. Years ago a spark plug blew out of my '96 Cobra, and the dealer repaired it with (reportedly) a helicoil. Now (perhaps 10 years later), that cylinder is misfiring. I've replaced the plug wires, and in doing so I noticed that the spark-plug boot doesn't insert all the way on the...

Hi all. So a spark plug blew out of my '96 Cobra the other day, of course damaging the threads in the head. The dealer's trying to fix it with a Helicoil insert. Any opinions on this? What about this Calvan tool that turns up in searches on the topic? And, if I have to replace the head...