When would you replace a Rectifier and how would you know it needs replacement. I have a Counterpoint NPS-400 and had it repaired by a reputable custom shop and was told that they do not effect the sound and either work or don't work.

Then I go onto Mike Es Alta Vista site (original owner of Counterpoint) and he has several levels of replacement rectifiers with notes on the different sound they produce.

I'm confused, do they or don't they effect the sound? How do you know when it's time to replace them?