sounds like you have all the symptoms. But make sure of one thing before you tear everything apart: make sure it's radiator fluid that's leaking into your cabin. IF it's just water, then the drain line to your Evaporator is probably plugged up with dirt/leaves/squirrel parts, etc. I know that you might think it's weird to have AC condensation leaking into the cabin at this time of year, but keep in mind that the AC is running every time you use the defroster.

Anyway, that's my slice of hapless optimism for you on this Christmas Eve. Maybe it's not too late to ask Santa to leave a heater core and accompanying mechanic under the old Christmas tree!