87 ciera coolant problems

The inside of my car always reeks of coolant, and my windshield is all fogged up. defroster doesnt do anything, so i go to wipe it off, and its all oily, like the coolant getting on my windshield. I would guess its the heater core. Just wondering if it could be anything else?

not really much else it could be - I'd go ahead and replace the heater core

thanks