Most Mercedes dealers won't touch an XF.

Chrysler dealers generally suck when it comes to XF's.
Due to low produce numbers very few techs were trained.

Maybe you can find a dealer that sells both or actually has an XF trained tech.

For a start, check codes and see what some of the XF gurus on this forum have to say.
Also, use the searcg function like crazy; this has probably happened before and been solved.