heater core question

[Superpromustang]

If it's not leaking too bad, then you can probably fix it with some stop leak, and the heater cores are inexpensive, it's the labor involved in putting it in, when I had mine replaced, it cost me $300, because they have to take the dash clear out of the car. And to answer your question about why it does it, is because the coolant is under pressure if there's any leaks at all it will find it and come oozing out, and since your heater core is right under the dash and is in junction with your defroster vents, it comes up on the windshield as steam and then condenses back to the liquid creating the nasty film on your windshield, hope this helps,

Kenny