If the door seals appear to be ok,then I would suggest a auto defrost issue.Likely causes are a failed defrost timer or a problem with the heater or drain sensors.When you do another defrost,make sure the freezer drain pipe isn't blocked.That's the pipe that drains water away from the compartment down to the evaporation tray ontop of the compressor.Fluffy white ice is a good indication of door seal failure.
paul
January 2012