Ignition leads

So a few weeks back I posted here about large mag drops and electrical noise
on the radio. Many posters prognosticated that an ignition lead was to
blame, and when the mechanic opened the cowling, this was confirmed- one
lead gone beyond repair.

He put all leads on a tester, and said the other 7 looked fine, so we
elected to simply replace the one bad lead, which cost $45 for the lead and
about $130 for the labor (2 hours IIRC). We initially siggested replacing
the whole harness, as 7/8 leads were original 1979 vintage, but the mechanic
siad, "why bother?"

A week later two of my partners are flying back from a short tripe
(basically one hour after the bird came out of the shop) and back comes the
magneto drop and popping sound. They find a mechanic, and sure enough,
another lead's shot. So now we're back to replace the whole set and keep the
two newer leads as spares.

Is the moral of the story that on any repair that involves multiples of the
same item (plugs, valves, etc.) to just replace the whole set if they're
more than X years old? We've also got cylinders reading 63, 68, 70, and 73.
If one dips down, do we just top the whole thing (it has about 1800 tach
time) or just replace the bad jug? Or do we declare surrender and major it,
even though it's a 100% part-91 airplane and the engine doesn't turn into a
pumpkin when the meter hits 2000?

I don't mind spending money to fix things once, that's just life, but
there's nothing I hate more than fixing the same damn thing twice.

-cwk.