culligan softener valve out of sync

I have a culligan "Northbrook 8" softener system that has given me excellent service since 1985. I have even relocated it twice! I now understand that this is a "cheap" culligan unit, but I can't afford to replace it any time soon! To make a long story short, it appears that the timer mechanism got jammed. When I discovered this, I was able to determine that 1. The clock was still working properly. 2. The unit had stopped cycling, or I'd have noticed when I did the laundry (all that water running!) 3. Now the unit appears to be out of sync. when the clock is in the "bypass" position, water is running. The only way to put it out of the cycle is to manually turn the gear that controls the cycle to the point where flow stops and unplug the clock.
This is a unit that works by subtle changes of water pressure that depresses the pistons. The clock turns a wheel which causes water to flow into chambers above the two pistons, which depresses them and controls the system. The pistons appear to be in good shape--even the particle screens are clear.
Does anyone have experience with a unit like this?
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