All of the lead weights I have seen attached to the usual reeds in pipe
organs were seemingly glued on with a dark colored adhesive of some
kind.  Over the years the glue looks like it would become brittle and
there would be a lead weight in the boot that fell off.

Maybe in theatre organs or for higher pressures they did something
different, but I have seen sets of Austin pipes, both new and repaired,
as well as other makers, all having the lead glued on, not soldered on.

Randy