[prairieschooner]

Clarke,
I would recommend that you replace the Sacrificial Anode on your Raritan Water Heater and see what happens. The Seaward does not have an Anode making it less expensive. No Guarantees but if the Anode is replaced at least the Corrosion will be suspended.
Here is a condensed version of how the Sacrificial Anodes work, as I have come to understand it;
When a Metallic Component is immersed in an Electrolyte it creates Voltage that is measured in Millivolts. The Sacrificial Anode is sized to create move Voltage that the Metallic Components in the Water Heater will. The Sacrificial Anode will be used up creating the Voltage needed to protect the Water Heater. Once the Sacrificial Anode begins to produce less Voltage than the Metallic Components then the Metallic Components begin to protect the Sacrificial Anode, this could appear as if the Anode is still in good condition while it is in fact not working. So as you can plainly see you should change the Sacrificial Anode at regular intervals (on a boat this should be every 3-4 months on the the items that are individually protected and 6-9 moths on the items that are tied together, normally refereed to as Electrically Bonded).