It could present a range of symptom from coolant loss, overheating, or even go as far as coolant and oil mixing in the engine and radiator both.
It looks like you might have a chance to catch it before then though.
Sorry that it's not better news, but experience tells me that's what's up.
One of the hints I see from the plugs is number 6 is greenish brown and shiny, and that is going to be where the gasket is the most rotted.