I have to agree... This is actually one area that the MM Warranty Act would protect you. As long as the DEF you purchase is API certified, there should be no issue.

Here is a link to what will be the DOE's DEF Locator... http://www.afdc.energy.gov/afdc/locator/def/

Some additional info on Motorcraft DEF... Ford recently signed a contract with Terra Environmental Technologies Inc. to provide the DEF that will be used as factory fill as well as what will be branded as Motorcraft for dealer and consumer use. Terra also holds exlusive supplier contracts for DEF with Daimler and Hino, and preferred supplier contracts for DEF with Volvo NA and Mack Trucks NA.