Wake up call. This is the first I've heard of Dex-cool related problems. A quick check on the web reveals serious engine repairs due to Dex-cool. This is Big. Looks like GM is trying to stay ahead of the courts regarding class action status involving thousands of car owners. Maybe too late already. Please tell me adventure_of_link that you do NOT own an affected GM car.
The following is from Wikipedia:
Organic acid technology
Certain cars are built with Organic Acid Technology (OAT) antifreeze (e.g., DEX-COOL), which is claimed to have an extended service life of five years or 240,000 km (150,000 miles).
According to the DEX-COOL manufacturer, "mixing a 'green' coolant with DEX-COOL reduces the batch’s change interval to 2 years or 30,000 miles, but will otherwise cause no damage to the engine."
Typically OAT antifreeze contains a red or pink dye to differentiate it from the conventional glycol-based coolants (blue or green). Some of the newer OAT coolants claim to be compatible with all types of OAT and glycol-based coolants; these are typically green or yellow in color.