Although a galvanised chassis may be desirable unfortunately any time and money you spend to maintain a vehicle does not increase the market value. Why would anybody look to give you 12k for yours when they can buy one with decent chassis for 3.5k?
You have an oil delivery issue, there's no quick fix it needs investigating. Unfortunately serious damage may already have been done if it is a "developed" habit!
"Clueless new Range Rover Defender owner-to-be..."
Don't worry the fact you call the Defender a Range Rover already confirmed to us you were clueless on them.