I'm asking question. If you have answer, please provide.
I hate to be one of those grumpy old men who says "search the forums", but seriously. This question has been asked literally *hundreds* of times.
There's a really good thread (which I can't find off-hand) that shows the damage from leaking caps, with pictures. Thing is that a lot of them will leak from the bottom, so just a visual "surface" inspection may not reveal the corrosion occurring beneath them. And by the time you start getting the stability and audio glitches (a common sign that the caps are starting to go) common in our Amiga's, especially A600/1200/4000/CD32, irreversible damage may already have occurred.
Then there's the aside that *it is just so cheap to do*, why would anyone not do this common preventative maintenance? Even if you lack the tools or knowledge to do it yourself, AmigaKit and many others will do it for <$40 USD per board. Not doing common preventative maintenance is like arguing that you shouldn't change the oil in your car "since you can't see it it must not be bad", right? Gah. :p
I've never personally replaced the caps in an Amiga (yet - A2000's aren't as susceptible), but as a former Dell field technician I have replaced hundreds of motherboards that fell victim to
"capacitor plague". (see link) Just do it, and rest easier at night.