There is a plastic piece in this cartridge that breaks and fails the rest of the cartridge.  This small plastic disk seems to act as a piece to tighten the action between the handle and the valve.  I don't understand why DELTA would place it's faith in this small plastic piece to last as long as the rest of the well built cartridge.  So I have to replace the entire cartridge because of a small plastic disk that couldn't cost more than 1¢.