This is normal as overtime the diaphragm gets weaker from moving back and forth so rapidly causing it to tear. The aerators are designed to be rebuilt two times before a new pump is needed. This kit is the complete service kit it comes with all the necessary parts to correctly rebuild the aerator.
The kit includes the magnet spacer and alignment shims these are needed to keep the magnet straight as the old parts are taken off and new parts put on, so on start up the magnet doesn't move and ruin the coils. Also in the kit is a new filter, bottom gasket, filter gasket, chamber block gaskets, chamber blocks, diaphragms, and screws.