I need help from the pro's diagnosing the cause of a leak under my console sink. The attached picture shows the source of the leak - where the water supply is connected to the cold side. I did not use any tape - pretty sure I read that you don't use tape on a metal to metal connection but maybe I got that wrong. I have tightened down on this connection a couple of times now but the leak remains and I am concerned about over-tightening. Thanks in advance for your help!