I had already gone to Mouser and sourced the caps above (in my case, 1000uF @25v) then thought I'd double check trying to reset the default settings. I'd previously gone to Settings > Sound > Volume Mixer and chosen the "Reset sound devices...etc." Reset button, but it did nothing.
As it turns out, Settings > Sound > More sound settings, clicking on the SoundSticks icon, then choosing Properties > Levels > Balance showed that the left/right speaker balance ''was'' out of whack. (In software.) Adjusting this fixed the problem. I have no idea how that balance setting became ''unbalanced'' -- I certainly did not do that manually.
Also not clear why clicking the "Reset sound devices to defaults" button did not reset the L/R balance.