My dealer, Crest

told me the same thing on my first diff. And it lasted 11k miles, they installed a new seal and fluid after 5k miles.
Took it in today for the recall, now their just gonna replace the complete diff. Service mechanic

kinda scoffed at the KARS III, but ended up saying he could care less and they would cover the new diff.
My service rep said when the diff arrived(they don't stock them???) he'd call me and be sure to have an 08 cts waiting for me when i dropped the V off. Looks like I need to be getting 2 gift certificates for the Lobster.