I don't think you need it to be replaced. I have a slight amount of air come
through also when I close everything. To me, maybe I am wrong IMEO, I don't think it has to be totally airtight. The UFS was created so that you equalize the pressure when you take a drag. That pressure pulls a small amount of liquid into the atty. I myself don't have any problems with the minor airflow. I am still working on getting the "perfect" settings but any way it works great.