[sdiy] Lifespan of Electrolytics?

[Joe Kramer]

Hi Folks,
    I recently got ahold of a Tapco 4400 reverb for cheap because one channel
was dead.  After chasing down a handful of 4136s and systematically replacing
each one, I came to find that the actual problem was a bad electrolytic in the
signal path.  The circuit board is dated 2/17/77.  I'm guessing that several
more of the caps in this board are marginal.  What is the expected lifespan of
electrolytics, and what are the effects of old and aging ones?  Is it worth the
trouble going through any old gear including synths that are past, say, about
twenty years and giving them a electrolytic overhaul?  Anyone have firsthand
(or secondhand) testimonials?  Thanks.

Regards,
Joe Kramer