This is from High School chemistry and that was a LONG
time ago.

I agree that it will be a corrosion issue.

When water enters such a joint two different metals make
up a battery. This can enormously accelerate corrosion
and is what happens to, for example, chrome plated parts
on cars. They get badly pitted quite quickly (not though
in Arizona). Modern cars do not use chrome I don't think.

Of the metal pair, the less "active" one is preserved and
the more active one suffers.

In order of activity Chrome is lower than Iron.

Copper is likely a nice material for such sleeves since
it is ductile and can 'flow' (I guess) into the wire without
too much pressure or too much damage to the original wire.
(You wouldn't want a sleeve that cut through the wire).

However, Copper has a lower activity than Iron and
so Zinc plated sleeves are use. In this case the Zinc
has an even higher activity than Iron or Copper and
so it is 'sacrificed' and the integrity of the cable is preserved.

For some reason, (I have no idea at all) the zinc must cause
some problem with the stainless steel (Iron, Nickel, Chrome and
maybe other bits alloy)


http://www.qsl.net/n9zia/electrochemical.html

http://www.lytron.com/support/galvanic_corrosion.htm

Google for [tin copper aluminium electrochemical potential]