Heater core leak? That sux. Did your coolant get all over your floor area underneath your glove box? Or did it drip outside like its supposed to? Changing it is not too bad but getting your fingers to disconnect the hose lines can be very tight. Some heater cores where you attach the hose come in plastic and can break or crack as you put on the coolant lines. I got the one that was made of aluminum so it would have more strength. Would really be a drag if you went through all that and still leaking because the connector cracked on you. Usually with a heater core gone bad, you get some STEAM looking action when you turn on the heater. Can smell the antifreeze too. You must have had a slow drip.