freezer part of refrigerator leaking water

I have a Whirlpool Refrigerator that water leaks from the freezer through the vents. I took apart the freezer and there was ice in the pan and in the drain. I flushed out the line and everything was good for a month and know same problem. I have been doing this every month or so. Any suggestions?

Thanks,

I just would like to add that I found other posts that have this problem, but it keeps on happening.

I did that and it works good, then it freezes up and water start flowing again. The bottom of the freezer, including the pan accumulates ice.

Any thoughts?