I am very reluctant to take on a restoration project because most of the parts are way beyond their expected service life. One can completely repair a unit, then have an unrelated failure soon after. Digging up original parts is risky because they are also beyond their expected service life. If I replace a failed component with a modern substitute, is the unit still "vintage"?

In general I find that customers are not prepared for the risk of serial failures of a unit and feel victimized when there is another failure.