Maytag side by side

My side by side coils (in rear of freezer) freeze up causing the refrigerator temp to increase. My 1st attempt at correcting the problem was to replace the adapt defrost board; this gave me a four month window before is happened again. My 2nd attempt was to replace the defrost thermostat, which yeilded a 1 1/2 month window. What are my next options?
Additionally, my adjusting screws for leveling sheared off over a year ago, which coincidently(?) was prior to the freezing coil problem. Also, when I firmly push the doors closed, I hear the door seals "hissing".
Lossing time, food and my mind. Please help!