I doubt it's capacitor related. My bet is also the ribbon cables - they are over 20 years old and were never made to last this long in a harsh operating enviroment.

Rather than "guessing" I would swap the sound board (first) with a known good one - or send it off to Beaky for checking. Replace the ribbon cables next - they are inexpensive really.

More damage can very easily be done by "fixing" things that don't need fixing.