I’m looking for some opinions on something I came across today.
Here we see corrosion on the inlet nipple extending down toward the water heater. No other corrosion was found at the water heater exterior.
Do you think this is a simple fix (replacing the nipple, replacing the failed dielectric) or is this 10-year old water heater officially toast?
Not a call you or any of the rest of us can make. If it’s ten years old there are probably other issues with it anyway just due to time, but this is not necessarily a situation where replacement is an absolute.
It looks like it leaked a little at one point so some of that on the lower portion of the fittings may only be on the outside of the pipe. The plumber won’t know until it is disassembled and you will be long gone by then. 
Great answer, Cameron. Thank you.
looks to me like a galvanized nipple, which is gonna naturally corrode when contacting any other metal.
Not your call, really should be a plumber’s call, but the fix is to install different fittings that are not galvanzied.
"Visible corrosion on the fitting on the water heater. Corrosion is the result of past or present leaking due to dissimilar metal corrosion. Advise a plumber reivew and correct as needed. "
You can always add also
Since the water heater is aged, corrosion can affect the connection at the tank in rare instances, prohibiting a simple repair. Only dissasembly by a plumber can determine the severity.
