Should I leave the heater box out?

Was it leaking on the carpet, or blowing on the windshield? Mine started leaking on my Polara when I took it out last week. It seemed to stop towards the end. Any chance the cold weather contracted the tube and core enough to make it leak? And after having cooling running through it, expand it back to seal? Just an unscientific guesstimate I'm the hopes of not pulling all that out of the car, as I drive this vehicle every day.