I just talked to a guy in the parts dept at the dealer where I purchased the car. He had never heard of XL-18. I'm really not sure if I need to just buy some of this stuff from Ford or go through the dealer. I did get him to verify the TSB on the lower control arms, so I've got an appointment next week to get them looked at.
If you go Over to the 2011+GT Tech. Forum, and at the Very top of the Page, there is a "Sticky Thread" about this Additive, and how to Order it from your Dealer