[Jake Raby]

The end of the spark plug is flush with the chamber. Exploded pistons and collateral damage from cylinder failures will easily do this.
If the cylinder failed you'll have a crankcase thats filled with coolant as the two will intermix at the point where the cylinder fails.

Being a 99, the cylinders are inherently compromised. See if you find any blue paint marks on the crankcase from the factory. It almost looks like overspray.