The half life is about 20-25 years, IOW about half of them will be needing replacement after about that time. Low temperatures during operation and frequent use both help extend the life. If in doubt, change the parts.
Hum in the amp or preamp can be an indication. Bulging caps, or safety plugs that are bulging are also good indicators.
Hum in the amp or preamp can be an indication. Bulging caps, or safety plugs that are bulging are also good indicators.