No water is disapearing from the radiator, and it's full of water plus green coolant.
And the water behind the plate is pure water.
That sounds like you're experiencing a condensation problem, not a coolant leak. Before you start doing any major disassembly, try this: Pour about a quart of alcohol into the crankcase, methanol that's used as shellac thinner, etc., not good beverage alcohol! Run the engine until it gets up to normal operating temperature without driving it- - - - -we don't want to put any load on the bearings with compromised oil. The alcohol will absorb any moisture and flush it out of the engine when the oil is drained. After the condensate is purged, keep it from accumulating again by getting the engine up to full operating temperature about once a week. That will keep water from getting to the point of puddling due to long periods of inactivity.
Jerry
