I guess from 2005 to 2008 Ford used a faulty spark plug in the 5.4L, 4.6L engines. When you try and remove them they break causing additional servicing. There is a FSB to help mitigate the problem but it appears it still fails a lot. Any way here is the FSB from another site:
http://www.fcsdchemicalsandlubricant.../tsb/06152.pdf
You can find lots of forums and chats about this. Most are staying you should replace the plugs earlier than later, but be prepared to extract the broken parts or get it done at the Ford shop then pay $$$. I think most people are out of warranty when this hits. I've just started to read into this as well as I just got a new 08 Expy.
There is also