Scoop on Moen is that you have to be the original owner of the fixture and have proof of purchase in order for the warranty to cover any replacement pieces for free. So I ended up having to pay for a replacement diverter for our fixture, but will be keeping our payment proof for the other bathroom we have that has new Moen fixtures going in (in case we ever need in the future). She said if it was new construction that you purchased with Moen, you'd send in a copy of deed or title showing you were the original buyers of the home when they were installed. We are not the original owners of this house, so we couldn't use the warranty for us.
Maybe that helps you, or maybe not? Good luck though if you are having any issues.