If you own a Ford F150 with a 5.4l, changing plugs can be very expensive indeed. In a nutshell, if they can not get them out within say a day using special fluids etc, the next choice is new heads.

So, my 08 with 90k, will keep them in until it won't run anymore. Any of the issues with XF in this thread pale in comparison. I think Ford should have a class action on this one. It has been going on for some time. Upfront, the dealer said 700 and up to 2500 for plug change out. I just have to believe a local small claims court would find this in the favor of the small guy.