Have you pulled the intake off to inspect the gaskets? The coolant in the spark plug tubes is always the gaskets as coolant flows through the front and rear of the intake manifold per intake / engine design. When I did my PI intake / cams swap, the intake manifold gaskets were completely shot giving me both coolant and oil in the spark plug tubes in all of the passenger side spark plug tubes. If you remember, at the time I was completely green to this engine and parked the car because the leak had gotten down to the spark plug firing pin on cylinder 3 causing a misfire.
That head and cylinder were in fine working order!!! They didn't need to be pulledThis is what a bad valve does, you can see for yourself which fares better
And no, you're still not grasping Occam's razor - The coolant would need to defy gravity and many other obstacles to somehow get into a vertical tube above the cylinder if the head gasket were the source.
And yes that's a placebo...err intake spacer:tongue: