Recently I had the opportunity to view a home that was just listed. I was asked to do a quick walk through and offer the sellers suggestions to improve its potential to sell. The hot water heater was about 12 years old and was not leaking but definitely showing its age. I suggested possibly replacing the hot water heater and I was asked the question: Will we get our money back? I politely stated there was no guarantee but replacing the heater would definitely help the selling of the home. Any competent home inspector is going to report on hot water heaters that are nearing or beyond their useful life. If you replace the hot water heater it is an non-issue or possibly even a selling point instead of a negative.
It goes without saying if the hot water is leaking get it replaced before you list the home.