I would bet that the coolant in still the factory stuff from 2004 and that the intake gaskets have no been changed yet.
I'd loook between the cylinder head and intake manifold to see what color the gasket is. If the gasket is black, that thing is a ticking time bomb to me. Giving that it's still got dexcool and the fact that the factory intake gaskets have a high failure rate past 100k miles. They make an upgraded aluminum style intake gasket to fix the issue forever. That would be the best time to flush the system and clean everything out aswell.
