Gregger
Living Legend
Great catch @Stillserving. Forgot about that thread. One of the reasons the problem and solution should all be posted in the same thread.
I shy away from using coolant sealing additives simply because of my own fear of having the stuff seal some small coolant ports inside the rad/engine but that's just a feeling and has never been proven by me. Since that fitting looks like one major pain to remove, I might have tried the additive option too. Keep us posted.