My freezer is leaking?

My side by side refrigerator is leaking from the freezer door. Inside there is a lot of ice built up on the bottom level of the freezer. I got it all away, but cannot find the defrost drain, as I think that may be plugged. I have found that the leak is coming from the area at the back of the freezer, behind a small grill where there are the cold elements. model # ASD2120DR Admiral, 21.7 Cu. ft. about 7 yrs. old