I would dfinately agree it is the age thing.
I just pulled mine apart for the same thing. It looked a little worse off than yours, looking at it, the composite material gets disintergrated over time b/c the water jackets are fully exposed. Most engines have a deck with only ports exposed. Once the material is weakened it looks like it allows the ring to move and then it starts to weaken as well.
I was boosting mine when it happened so it really pushed the ring out and it sat overnight and hydrolocked. luckily I caught it quick and knew what it was and turned the enginge backwards to allow the coolant to escape. Yes I could have pulled the plugs but my intake makes that a little difficult
so I drained it and started it to get it onto the trailer. now for the real fun