I'd like to step back a moment and mention that if you are using one of the many coolants on the market that mixes with any color it won't cause sludge if mixed with Dex. Being that this is the cold season for most of us, it'* a good thing to keep in mind that there won't be any adverse effects of using a coolant that will mix with Dex w/o issue. Most coolants on the market will mix, check the labeling.
It is a good idea to maintain your cooling system per the factory recommended timeframes.
Dex is oat based and tends to sludge if air is introduced/allowed into the cooling system.
00 Regal GS: All kinds of cool stuff.