I think anytime you can do some cheap maintenance while you are in a project, its worth it. They dont cost much and its all apart, why not? They may not "need" replacing, but they will be worn down in size. The main reason I did mine was because one became so worn it was stuck right into a plate opening. So since I needed one, I got all new. But comparing showed that others were worn down too. I think Mercon V may treat them better than the Mercon III did.