I agree with chopper. It is a better practice to keep a visual inspection on your links (at least once each time before heading to the field). If the ball links start getting sloppy, or if you are able to easily pop the link off with your finger, replace the plastic. You'll want to keep the links good and tight anyway as it will add to the overall handling of the bird.

Just my .02, I change my plastic ends yearly, as it only cost me about $9 to do the whole bird.