Having to replace the intake manifold gasket at 43K in my wife’s 2005 Bonneville I decided some research was necessary on Dex cool. What I found is the best example of planned obsolescence I have ever witnessed. Introduced in 1996 it has changed very little if any since then. As a coolant it works until it is introduced to air, according to GM, IE you have a slight coolant leak and the system runs low, it causes the coolant to deteriorate rapidly. The coolant does not have to be that low but just a slight loss of volume in the radiator can cause problems. The intake and manifold gaskets are also unchanged to prevent the coolant from causing a problem. There was a change in the gaskets a few years ago but it had nothing to do with coolant contamination. Dex cool is a organic acid technology and when it breaks down tends to drop out inside the engine in the low spots. Dex cool can turn to a gooey, muddy, orange corrosive gel that will attack the plastic surfaces and the gaskets causing leaks. In severe cases it can clog the heater core, radiator and in some cases the water pump. . In severe cases this can harden and actually push the gaskets out of place. If air was in fact the cause of the problem why doesn’t the coolant in the overflow container turn to sludge? Basically all 27 brands of coolant start out the same it is the additives that are added for corrosion protection that cause the problems. For years this protection came from silicates. Recently more of the brands are using OAT and a few are using both. The actually cause of this problem is unknown and the only cure is to replace the Dex cool with a good quality green antifreeze and replace it every 2 years. Why it happens to some vehicles and not others is the question that is unanswered. GM says that the radiator cap may be the answer a cheap form of prevention and I do recommend replacing the cap with an aftermarket when doing the first flush. Even if your coolant looks fine it may be carrying a small electrical charge which will cause corrosion. Check the parasitic voltage with a volt meter, positive lead in the coolant and the other to ground you should have very little if any voltage. If voltage is present replace the coolant and check the engine grounds. I install a ground wire from the radiator to the body, a little anal perhaps but remember the radiator has very little if any metal to metal contact. Rubber hoses and mounted in bushings. There is a class action suit for this problem but that is for a later date.Before I get a ton of Emails, yes I did say aftermarket radiator cap if there is a problem with the GM cap why use another when a aftermarket will work, perhaps better.