[Rich in Tucson]

Just a clarification from an old biochemist messing with metals in and on old Fords et al.: Sodium (or Potassium) Hydroxide solutions (lyes) are strong alkalis (not acids) and given enough time and at particularly elevated temperatures will attack and dissolve Tin, Aluminum, Zinc and Cadmium, Chromium, and Copper. But not iron or steel, and therefore they are great cleaning agents for most metals (Oil Eater is a great carbon remover for pistons and valves IF used judiciously; it will remove carbon at a far greater rate than it will remove Aluminum from pistons for example).

If I had a flaking old tank sealer on a degraded gas tank and could not afford to cut it open for restoration I would not hesitate to clean it with lye (or similar alkalis) with frequent monitoring to determine its effectiveness despite knowing that I am slowly removing any (if any) residual original Terne plating. Then a "modern" sealer could be used if trusted (I frankly don't know) or scrupulously avoiding any addition of moisture in the gas tank with perhaps the addition of a top end oil to the fuel might prolong the further rusting of exposed steel in the tank.