Just to give a quick update, I finally got around to attack the leaks and found that the gaskets for the temp sense valve, impeller lid, and the three way tube valve thing were all shot. And if that's not bad enough - holy rust, there's a lot of sediment collecting at the bottom of the pan! I can't tell if that all came just from the radiator or inside the engine too (I dread the latter), and the impeller, including the housing and all pipe joints touched by Coolant are totally rusted. I'm thinking of taking a wire brush and sandpaper to everything and do some kind of engine flush. Speaking of which, can someone suggest a reasonably easy method to flush all the rust and gunk out without taking the engine out? My spine and joints have declared war on me..