Lets be clear. There was lots of good advice presented here. But, that is all it is, advice.
There is such a thing as preventive maintenance in cars, electronics, etc. If one wishes to keep an item indefinitely, then preventive maintenance is important.
If upon visual inspection the capacitors are bulging or obviously leaking material, then it is past time to replace.
If the amp is over 15-20 years old, but the caps appear okay and the amp is operating well, then, it is up to you. I wouldn't replace the caps unless I notice issues or if I had the funds to replace the caps in advance of issues.
Like cars, you are warned most times of issues before they become really serious. Therefore giving you warning. whining bearings, leaks from the water pump. All indications that you need to do something.
If the amp works, the capacitors are in good shape and not leaking, then you don't have to "do" anything but enjoy. But if you have the budget, it can't hurt. However, for solid state electronics, it is also a very good idea to remove all output transistors and test them and replace if they test outside specs, and very importantly, replace the mica insulators with new and also the silicon heat compound. This dries over time and causes output transistors to short against the heat sink and fail the amp.
I do this on general principle whenever I get older equipment.
Some amps are easy to work on and other's (Mark Levinson 23.5) are a serious pain in the bottom. Great amp, but OMG what were they thinking?
enjoy
