I use mason jars for my homemade jam. Yes the lids are made for one time use - for food. According to what I've read the rubber ring vulcanises when heated. For jam the jars are put in a gently boiling water bath for 15-20 minutes. You might try boiling the lids for a while to harder the rubber. The ring isn't meant to hold the lids tight for jam storage. That step and the created vacuum seals the lid tight to glass. The retaining ring just holds the lid in place for the water bath.