Thanks Tim, you are the best.
So, rings means a disassemble huh? Oh man, no time for that. I didn't see any scoring on the cylinder walls of #4, actually that #4 looked smooth as glass but I'll take a second look.
And no signs of a busted Hg, but it was doing all the tell-tale signs: Coolant out the overflow after driving on the highway for more than a half hour, and tiny bubbles(isn't that a song?) you could see under the radiator cap. Maybe I didn't burp it enough but I burped it a bunch...
Oh well, we'll see what the head shop says.