Dave,
these people are worth talking to....
https://www.southboundtrimmers.com/In Stockbridge.
I've bought replacement studs for the hood from them! When I visited they were re-upholstering a Porsche 911, so probably not cheap.
As to the leather/Vinyl question, things have evolved. Instead of vinyl there are a number of artificial leathers, most are water resistant, yet breathable. Mercedes call there product Artico (Artificial Cow) and if I were to reupholster Tarka I'd seriously consider using it for everything other than the seat faces.
Peter
