Standpipe fix

I have a frostfree standpipe that has apparently developed a leak. I heard the pump running this morning when no water had been used. I have all the standpipes equipped with 1/4 turn ball valves so I can leave them in the open postion - much more convenient operation. Mentally retracing my steps yesterday I remember cycling one of my standpipes open and shut a few times. It appears that it is leaking when in the shut-off position.
1. Can it be fixed without digging it up? 2. I have one that hasn't been used for many years (stock waterer). It is solidly locked in the shut-off position. I tried to open it this spring and it won't move even a fraction of an inch.
Because of number 2, I have taken to cycling these vavle regularly - looks like that caused my leaking problem.
Harry K

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