When to replace wearable parts?

[Maximum1]

This may be a silly question but what the heck...

When to replace wearable parts? When it comes to recoil springs, ejector and firing pin is it better to replace them after a certain number of rounds fired or wait until you start to encounter problems (a scary thought).

I'm somewhat surprised gun manufacturers don't list recommended replacement schedules in the manual or on their website.

 

[Majic]

Springs will wear, but ejectors and firing pins shouldn't wear. Some manufactors will give you a round count as to when the springs should be replaced.