Do water lines that contain lead need to be replaced if it doesn't flow out of a valve that I normally drink out of?
The water supply piping in our house is copper sweated with lead-tin solder in 1971. We have lived here since 1978. Dallas water is slightly basic (ph 8 or so) and has some minerals in it that I believe would react with the lead to form an insoluble passive surface. We drink water from the taps.

I  don't think you have anything to worry about.