I have a Balboa spa pack inside an Infinity hot tub.

The union to the left of the spa pack has a split nut union covering it. This leaks when the jets (three of them) are set on the highest setting. Then the water runs out of the split nut union. If the jets are on low it drips occasionally. If the pumps are not on, nothing leaks. I'm wondering if the entire union needs to be replaced, or if this might be a faulty o ring. Any thoughts?

Thanks in advance,