The owners manual for the 2009 Cadillac CTS is at http://www.cadillac.com/content/dam/Cadillac/Global/master/nscwebsite/en/home/Owners/Manuals_and_Videos/01_images/2009_cadillac_cts_ctsv_owners.pdf
It recommends the use of TOP TIER gasolines, and then says for customers who do not use it, they recommend adding one bottle of “GM Feel System Treatment PLUS” to the tank at every oil change.
Whether you agree or not with what the manual states, it’s a far cry from what the service tech recommends.
Don’t forget that most service techs are under financial pressure or orders from the management to recommend such services.