2001 Dodge Ram heater core

The only fix for a leaking heater core is to replace it. If antifreeze is getting on the inside of the windshield, it will feel slimy or oily. The level will be going down in the reservoir too. If you look under the hood on the passenger side of the firewall, there will be a 4"-long rubber hose with a 90 degree bend in it hanging down. That's the drain tube for the air conditioning system. If the heater core is leaking, there will be antifreeze dripping from that tube.

If it's just water on the windshield and you're not losing coolant, that drain tube is likely blocked and there's standing water in the drain pan under the heater core. Squeeze that hose to open it and see if some debris can be dislodged.