Hot water shutoff valve slow leak

I live in a condominium and have problem with the hot water shutoff valve in the kitchen, under the sink. It is slightly leaky, for now just a couple of drops per day. The next shutoff valve before it is the main shutoff valve that covers several floors in the building.
Recently the maintenance people shut off the water for the entire building, and I used that opportunity to replace the washer in the valve. However, it continued to leak. It leaks along the thread that is visible when the valve is fully opened.
It leaks more when it is open half-way.
Replacing the valve is expensive proposition. It would require to shutoff water to other residents and it would be necessary to use a torch to unsolder the valve and replace it with the new one.
Is there any substance (kind of a glue) that could stop such minor leak.
The problem is not yet serious but it is annoying.
Thanks for any advice.
A.
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If I understand you correctly, I believe there is something called 'Packing' that they use on the valve stem. You probably have to replace that to stop the leak. If the cap on the valve has sides like a nut, you might get a wrench and try tightening the cap gradually. Good luck with it! Des

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