All SMD electrolytic capacitors must be replaced, no doubt about that.
Through-hole capacitors might be in need of replacement. They are used as voltage ripple filters in spots where the power consumption is bigger, that's why the larger units are near the power connector and very near the floppy power jack.
As all through-hole capacitors, those might not leak, but will dry internally over the years. Bulged capacitors and ones with shortened plastic labels suffered from overheating, indicating an urgent replacement.
Pretty much the same as in pc motherboards (but those fails spectacularly sooner). Blame crappy chinese capacitors.
The bad SMD units will look with a bulged dome, or a wet/oxidized/dull pad.
But even if none of the visual effects are shown, the bad behaviour of the Amiga will point to those.
