NO... Never mix DexCool (orange anti-freeze), with regular Ethylene Glycol (green anti-freeze). Dexcool is a no silicate based, organic acid technology (OAT) anti-freeze. G-05 as used in Chrysler's and some fords if I recall, is a hybrid OAT, known as HOAT. They are not compatible.
In order to use Ethylene Glycol (green anti-freeze), in a Dexcool equipped car, as mentioned a complete system flush (done by a machine), would need to be done.
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Actually, funny you should mention that as some Northstars with 4T80E transaxles (in the previous gen STS, Eldo's, Bonneville GXP's), would have core plug leaks. But you could never follow it by smell and on a warm, operational engine, it wasn't visible because it got burned off on the hot engine block and the exhaust cross-under pipe (they run under on those, instead of over as is usually standard on wrong wheel drive transverse applications), as it leaked. And of course, if you've been under one of those, you can't even fit your finger between the engine/pan, transaxle pan, and exhaust cross-under, so it wasn't something you just shine a light up and go "oh, there it is..."
You had to wait until the engine completely cooled (I mean like sitting 8 hours, overnight, etc), let it drip, and then trace it back up.