Vintage Synth Repair

Archive Sound promptly sent out key buffers for my benched Prophet 5,
and I promptly put them in.  Then I found out they have a top and
bottom, so I get to do it again (won't take very long).  Even without
making sure they're all right-side up, the change in feel is
phenomenal.  And, I got to tweak the keys so they're all even, etc.

Meanwhile, I find that someone has earlier butchered some of the
J-wires.  Specifically, some of the wires have been replaced with
soldered-on replacements that look terrible and, in one case, the
solder let go.

What material is best for replacing the J-wires?  And is there a
recommended technique for attaching them so they're mechanically
robust (lead-tin solder is *not* mechanically robust)?

Once again, thank you all.  Surprisingly, there seems to be nothing in
the P5 repair manual regarding the keyboard.  I guess techs of the era
were just expected to know their way around Pratt-Read keyboards.

Thomas