The reality about dex is it will get gunky like oatmeal if air is in the system. Other than that, it doesn't really hurt the gaskets. Most manufacturers switched to plastic based gaskets and all found degradation in short periods of time. Ours are no different. You'll find that around the coolant ports, they typically bow in. However, I have also found bowing by intake ports that has no coolant in the area. I've also swapped out to green with serious flushing etc and within 20K when I pulled the intake off again....bowed coolant ports.
You should perform the maintenance on the system....based on age. Personally, I fill with Anycolor as it's the most common coolant available and then there are no worries if either green or dex was in the system previously.
