I guess from 2005 to 2008 Ford used faulty spark plugs that when they are tried to remove will break causing more servicing. The TSB has some ways to help mitigate this but it still seems to fail a lot. Here is a post from another forum that has the TSB. Lots of treads and forums are talking about this headache. I've just started to dig into it.

The TSB is attached to this thread near the bottom.

TSB