Ice build up and leaking water

I have a standup frost free freezer that has constant ice buildup, then slowly melts and I’m left with a puddle on the floor. The water isn’t a big deal because the freezers in the garage. My concern is, it’s completely filled with breast milk, which is priceless.
It seems like there is a gap in the seal at the top because that’s where the ice melts. As it drips down the inside of the freezer, it freezes and leaves the inside covered with ice and some water manages to get by and leak out.
Can anyone help?