Here’s some advice if you have a leaking pneumatic tire:
One of the four tires on my garden cart had a bad leak. Every time I wanted to use it, I had to add air. The next day it would be flat again. I assumed that the inner tube had a hole in it, so with significant difficulty, I removed the tube, added air, and submerged it in a bucket of water. To my surprise bubbles appeared not from a hole in the tube, but from the valve stem. I happened to have an extra valve, so replaced it. That solved the problem, but it would have been so much easier to test the valve stem before I went to all the trouble of removing the tube. So my advice to you is that if you have a leaking tire, fill the tire, and then place a drop of soapy water over the valve stem. If you are lucky, bubbles will appear and the fix will be easy. You can order a tool and replacement valves from Amazon Prime: Slime 20088 4–Way Valve Tool with 4 valve cores ($3.99)
Now that I think of it, perhaps the reason that the valve went bad was that it had no valve cap. If that is the case also with you, you might consider ordering valve caps as well: Samikiva Black (30 pack) Tire Stem Valve Caps ($3.99) (Or you could call me—I have lots.)
I hope this solves your leaking problem.
Stan, The Tool Man