Here is a very good example. My Denon DCD-2700 doesn't anymore read disc as normal as before. It will take sometimes a few seconds to minutes. Sometimes you need to power Off, then On before it reads.
Last night, i changed all the digital caps with whatever good caps i could get, Silmic, Gold-Tune, Oscon, and Wima. After the change, now it reads much better (say 90% as good as new). The added bonus is that it also sound better.
So before thinking of changing the lens of your CD players, read through the link.