First of all, I just found a Dexcool problem with my car. I changed the oil and transmission fluid this morning, and while changing the oil filter, I found some sticky gooey waxy buildup on the screw on cover. I found this before, and used carb cleaner and a rag to remove it. I have no idea why I did not recognize it the first time I changed the oil. Since I had just changed the oil a little over a week ago, I knew it hadn't been on there long. Then it hit me. Dexcool. I looked above the filter cover, and sure enough there was a coolant hose connection there, with a lot of brown waxy buildup around it. It had been dripping down on the oil filter cover. I knew I had to get that stuff out of there NOW. I removed the plastic cover from underneath the radiator ( two 13mm hex head bolts and three Torx screws) Under the plastic cover, a metal rail runs across that area. It will be difficult to get to the lower radiator hose. But I did find a way to get the Dexcool out.
I disconnected about a 6" long hose from a fitting on the engine that goes to the reservoir tank, connected a long hose to it, stuck the other end of the hose in a clear plastic one gallon jug, started the engine, turned the heater on and let it run. I kept pouring distilled water into the reservoir, and the engine kept pumping coolant through the hose and into the jug. The first gallon was really dark brown, then next gallon was lighter brown, the third gallon was almost clear. So now the engine is full of distilled water. Yes I know plain water will boil at a lower temp than coolant, but I don't plan on going very far with it. Just enough to circulate it, then I will repeat the same procedure again to make sure I got it all.
At that point I'm going to have to find a way to drain it so I can put more coolant in. Which side of the car is the lower radiator hose on? I couldn't see a drain anywhere. Since GM does recommend replacing that stuff every 5 years, there must be a way to drain it out.
After I get through flushing the system out with distilled water, I'm going to remove that hose that was dripping down on the oil filter cover and see how bad it is. It just has a clip on clamp on it. Replacing that with a worm drive hose clamp after cleaning things up may stop the leak.
I have seen posts asking about a way to bleed the air out of the cooling system. I don't know if there is a bleeder valve or not, but it is not necessary. Just start the engine while filling the coolant tank, and let it run a few minutes, till the bubbles stop. The coolant tank is the highest place in the cooling system, and any air in the system will come out through the tank.
Here is a link to a bunch of people who are anything but happy with Dexcool
https://www.consumeraffairs.com/automotive/gm_dexcool.html