Fuel cap details

Trying to repair/restore the fuel cap. As attractive as the design is the use of a roll pin as a hinge for the fuel door is not the best idea and over the years the harder metal roll pin has worn the body causing elongation of the original hole, the fuel door sagging and not staying locked etc. A more permanent rethink is needed here so I would be curious to see if anyone has tackled or tried to improve the design/hinge? It does appear also that the inside of the fuel cap has not been chromed (which is visible on photo 0424) and must have some sort of other surface due to fuel. Also on the last photo corrosion is obvious on the neck leading down to the tank and I would like to remove this but not sure what to do as grinding it away would also remove the surface coating (whatever coating that may be). And with no coating at all petrol may cause further issues on the bare alloy...