OT: Some kinda epoxy or sealant?

I'm assuming that the leak is in an area where a Fernco coupling won't seal it?

None of these sealants specifically say "bronze" but you might be able to call McMaster-Carr and see what they say.

You can try, but I'd replace the valve. Funny you had that experience, because a few weeks ago I put in a new bathroom sink faucet fixture. When the water was turned on, same thing happened. Barely visible pray from the one side of the gooseneck. Couldn't even see the hole. I rubbed some setting compound where it was coming from, and that fixed it. But it's not under constant pressure. In your case and mine, something was wrong in the casting process.

If you can shut off the water and dry the area, two part epoxy might work. I'd wire brush the area, and mix up some of the 24 hour kind. Might even put some metal over the epoxy, much like the car bondo guys do. Some bondo, and then fiberglass mesh over that. But epoxy and metal. Might buy some time.

Short term, JB Weld may work. Long term, I'd replace the valve. May have been imperfect casting that eroded over time.

if the incoming line is PEX or copper use sharkbite coulings and valves. just cut the old copper line and snap in the new sharkbite..

super easy to use and they can snap apart in the future if you want to make changes..

they even have a sharkbite repair coupling for copper.. its extra long to patch a leaky copper line from say a pinhole leak....

I was in Lowes a few days ago and saw a display for this:

Hi, Thanks for every one. I got hold of "JB Water weld" and this "Fiber fix". On my next time out at the cabin will try both at the same time and see what happens and will report back.

Tony-

Is there a chance the hole is in a spot where there are no moving parts behind it? If so, you might be able to plug it with a small sheet metal screw. Perhaps a fiber or rubber washer under the screw head would help seal it.

Fred