"DEX-COOL"(tm) is not a specific chemistry. It's a GM extended-life coolant performance spec. GM Mr. Goodwrench DEX-COOL(tm) (made by Texaco originally, but now supplied by Chevron) contains the hydrated potassium ("K") salt of 2-EH as its OAT component. Prestone licensed DEX-COOL(tm) uses the hydrated sodium ("Na") salt of 2-EH and further lists the hydrated sodium salt of neodecanoate as the OAT components. Since Bill of Utah used the Prestone version, Na contamination of the motor oil would be expected if the engine was one of GM's notorious internal leakers. Fortunately, Bills last update tested negative for glycol contamination, so the Na was expected leftover from the previous Mobil Clean 7500. Had the report come back positive for glycol, it would have coincided perfectly with Prestone DEX-COOL(tm) contrary to Michael's analysis. Congrats, Bill - you dodged a bullet.