the important issue is whether or not bubbles are moving down the tubing. If it is just one bubble sitting in the tube, tumbling around, but not moving down the tubing, it is not a problem. if, however, it is an air leak between the flexible tubing and the cane, and little bits of the bubble are constantly moving down the tube with the beer, it is a problem. don't confuse CO2 bubbles with this though. tiny bubbles of carbonation coming out of suspension is not an issue and is normal. The way to tell the difference is to squeeze junction and if there is an air leak, you will find that if you squeeze it one way, the bubbling stops and if you squeeze it another way, the bubbling increases big time. If that is the case, remove the flexible line and cut off the bit that was stretched by the cane; starsan the end of the cane and push the tube on as far as you can get it being careful NOT to break the cane as they get a little brittle where they heat and bend it.