A/C leak

Welcome to 2CarPros, That valve can be replaced but not without doing one of two methods. The valve is almost identical to a tire valve and if they set a long time the seat develops an indent that may not line up again if disturbed. A couple things to try before that would be to use a punch or similar to give the valve a couple quick taps, you want it to just barely open and blow out a tiny bit of R134A and see if the seal makes a good seal, If that doesn't work add just a quick shot of R134A into the valve to see if it clears any debris off the seal on the valve seat. If neither of those work you will need to replace the stem.
There are two methods to do this, The first is to recover the R134A out of the system then replace both the low and high side valves with new ones. The other method uses a tool that you might be able to find as a loaner at a parts store. It allows you to remove and replace the stems without needing to remove the refrigerant first. There is also a cap you can get that you apply a bit of sealer and screw in to seal the port above the valve.