going in for an oil service next week and as its a 53 car it would be a good chance for the tech to have a look for cracks. Is good will repair 10 years from registration date or build date?

From first reg date, i.e what is written on the first page of the log book. You also need to be aware that the garage doing the repair must do it within one month of the goodwill being authorised. This means if there is a 3 month wait, the garage have to delay your paperwork 2 months to buy some time. Just pointing this out as most bodyshops have a long list of claims on backlog, and the 10 years is ticking away. Choose your bodyshop wisley.