The rust is endless. Is anyone familiar with the Ship of Theseus? That's what this project brings to mind. So Theseus owns a ship, and being the loving ship owner he is, maintains and replaces what needs when it needs it. Eventually, all the parts have been replaced. If Theseus were to keep all the old parts, and reassemble them, he would have one really junk ship. In essence, that is his original ship. Yet he has a new one that has been his the whole time. Is his ship even his ship?
In reality, those questions do not matter much. Our customer will be getting a spiffy looking BMW back, be it original or not. The owner and the things they do are what make the car what it is. Man, machine, experience. That's what we are concerned with. Not the numbers.