The new Moyer 502 flange pump you ordered has no snap ring at the impeller, no grease cup, and no gasket. Only a tiny O-ring. It's better to have the rebuild kit on hand in case you develop a bad leak, then you can fix it on the spot instead of waiting several days for the kit to arrive. The kit does not include a new pump housing or backplate. It does include new O-ring, impeller, bearings, seals, shaft, grease, and directions.
https://moyermarine.com/product/repa...p-csob_00_461/
If your experience is like mine, you have four years before you will need to rebuild the pump. But I run the A4 100 hours a year or more. Replace the impeller every two years, more if you use the engine a lot. The snap ring on the old pump was there to keep the impeller from wearing out and forcing water past the seals.