small leak (drip) behind the hot water tank.

I had a similar leak. Thought it was a fitting. Turned out the tank had a bad weld right on the seam and it was leaking (pin hole leak only with pressure and temperature in the tank) The water ran down the foam and came out by the cold water inlet fitting.
Ordered a new tank and when it arrived it was damaged. Ordered a second one and it was also damaged. Third time was the charm but it took a month.