It isn't, but for some reason you posted your thread in the forum for dealership and warranty issues. Submariner409 moved the thread to this forum (the 2003-2007 CTS forum).How is this a dealership or warranty issue?
Where do you think you've found Bilstein parts for your CTS? According to Bilstein USA's website, "Thank you, your search will affect future product development at BILSTEIN. Unfortunately, at this time we do not make any products for this vehicle." BC, D2, and KSport do make coilovers for your car - they are all the same cheap Taiwanese dampers marketed in different colors with different names. KW sells their Variant3 coilovers, which cost more than twice as much. Belltech markets the KW line in the US, and guys have picked up the KWs from Belltech for ~$1800 (compared to the ~$2500 KW list price).Anyway Bilstiein has an upgrade coil over kit.