For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

Vehicle Care
California Proposition
65 WarningWater Pump Cleaning and Inspection Engine Cooling Coolant Pump
Cleaning ProcedureCaution:Do not immerse the water pump in solvent. The solvent mayenter the water pump's permanently lubricated bearings and causepremature bearing failure.Remove the old gasket material from the water pump sealingsurfaces.Clean all excess dirt and debris from the water pumphousing. ...