Originally Posted by BIchselmnop
...I know that has been replaced at least once and the DexCool was replaced with the Prestone Dex.
The upper may have been replaced but perhaps not the LIM gaskets. If you are sure you have an internal coolant leak, my suggestion would be to tear it down and install aluminum frame LIM gaskets ($60). While it is apart, you can examine the UIM carefully for evidence of softening around the EGR bore. If the plastic is still sound, you could just replace the UIM gasket ($40) and add a heat shield ($10-20) for the UIM. Or, to be done with it forever, change out the UIM using the APN UIM kit for $115. For your newer LIM, you might consider having the base of the APN stovepipe machined from .749" to .624" OD to provide the largest insulating gap between the hot stovepipe and the vulnerable plastic.
Finally, those of us that think any Dex is bad Dex would recommend you flush and fill with the yellow "mixes with any color or type" extended life coolant.