Update

The system has been stable for about a year.
I replaced my Centaur Carbon in November.
I have had various drip leaks between the nipples connecting my bypass valves with my flexible hoses.
The galvanized nipples corrode and are not ideal.
The Fleck 7000 with male bypass assembly connections seems ideal.
Maybe I can replace my other valves with the 7000 eventually.
I noticed dripping from my MTM backwash line and disassembled and cleaned the valve.
The problem may not have been corrected.
I may have to replace the seals and spacers. I hypothesize that the spacers warp due to chlorine contact.
It seems I replace those in contact with the chlorine every year or two.
I plan to divert back washing from the three non-salt using tanks to irrigation in the next day or so.
This should reduce load on the septic leach field.
Other than needing to replace the seals and spacers the chlorine-retention-calcite/corosex-MTM-Centaur Carbon-Softener Resin combination seems to work well.