88 johnson 140 over heat

[thebottomfish]

Well I wish I was posting lovely things about my boat, but instead it's just more issues with my motor...and I'm determined to get to the meet up in August at tices shoal(slipped in the Metedeconk)
So I over heated the johnson, it keeps kicking in to slow mode within ten minutes of leaving the dock, happens at idle, or WOT doesn't matter.
I took the cowl off to realize the starboard head is way too hot, I know the hand method isn't the best but I can't even hold my hand there for a second, vs all day on the port side head.
Pulled thermostats same thing, no change, water pump is new, compressed air through every water hose, can't find a block so I pull the head to clean the water jacket, some build up but nothing bad to impede flow.
Until I find this white gunk that looks like epoxy. I had mentioned it in another thread but now I realize that it's in what I think, is an internal water jacket
I've attached pictures one of the thermos housing where you can see the white junk and then one where it exits at the bottom of the head, the rectangular opening. Hoping someone can help me figure out how to resolve this...I'm thinking the head cover is overheating because there's no water flow through that hidden passage, tripping the sensor but the head itself isn't overheating...thoughts?