To check the heads there are few ways to check :yes look at the outside for any signs of leakage ,this may be the most common is to check the oil for antifreeze or get an oil analysis and I also heard of getting the heads pressure checked at a shop,never saw this done but have heard of it.I once owned an 97 suburban with dex cool it actually ate through the intake manifold (it was a plastic manifold ) there were little pit marks in the plastic that was leaving in a little bit of antifreeze ,you could smell it in the exhaust ,it smelt sweet also in pa we have to do an emissions test(tail pipe) once a year and the hydrocarbons were high but to answer your question about this dex cool some people have problems and some people don't but I do hear a lot about it ,gm did change there gasket make-up a while back to address this problem and also a lot of mechanics change back to the greenish/yellowish antifreeze. Hope this helps .
