The existing gas water heater was leaking, which indicates some sort of breech of the inner tank.  The unit must be replaced at this point.  Typically, you are lucky to get 7-10 years out of a gas water heater, and this one was well beyond its life.  It was a 30 gallon Richmond – I replaced it with a 29 gallon model ($359 @ Menards).  Because it was about 10 inches taller than the old unit, I needed to extend the plumbing supply lines a bit.  For the connection to the water heater itself, I used stainless steel flexible 3/4″ supply lines (about $10 each) to make an easier installation and easier disassembly  in the future (if necessary).  I have a flat rate for water heater installation, and the process takes about half a day.  Call if you’d like more information: 419-212-3200