Although your thread indicates that you posted the original message on Wednesday morning, it didn't show-up to me until bedtime Thursday evening.
I'm not familiar with Culligan brand softeners but as it is over 20 years old, it will at least be due for a valve rebuild to renew pistons, seals and 'O' rings. 20-25 years is a long but not unexpected period before requiring service.
My softener required rebuilding within 15 years as the chlorine in my municipal water caused the soft components to degrade more rapidly. At the time of rebuilding, I also replaced the resin as the chlorine had also degraded the resin which resulted in reduced softening capacity and high pressure drop through the unit.
Although rebuilding a valve is usually a relatively easy job for a DIYer, depending on the valve, obtaining replacement parts maybe the most difficult aspect as you're likely limited to obtaining parts directly from a Culligan dealer. With proprietary equipment, you're at their mercy for cost and whether they will assist or instead, attempt to force you into a new system.
If you can post the valve model number or a photo with the cover removed, someone here maybe able to provide further recommendations including whether it is worthwhile to repair or to consider replacement.