I recently had two spa gate valves leaking from the seal around the stem. The piping and fittings on both sides of the valves was so tight and congested that I couldn't see a way to cut it out and replace it with piece of piping.
After draining the spa, I pushed the valve down about one inch. Then I drilled a 3/8" hole in the top and injected 3M 5200 into the hole with a caulking gun. Then I pulled the stem back to push the sealant into the stem packing/o-ring. After letting it cure for a few days I filled the spa. No more leaks.
