Do not add anything to the oil. The recommended oils meeting the dexos specification are all that is needed for good performance and engine protection.
Engine oil system flushes are not recommended and could cause engine damage not covered by the vehicle warranty.
#99-04-20-002H: Information on Driveline Clunk Noise - (Apr 11, 2013)
Subject:Information on Driveline Clunk NoiseModels: 2014 and Prior GM Passenger Cars and Light Duty Trucks This bulletin is being revised to add the 2013-2014 model years. Please discard CorporateBulletin Number-99-04-20-002G (Section 04 – Driveline/Axle).Important:The condition described in ...