Possible to repair GBB mag flow valve?
 

I have a KSC USP mag where the flow valve leaks from both the exterior button and from the actual valve/gas port on top of the mag. I have tried several silicone oil applications and working it into the valve from the side and the top but it still leaks. What is the cause of this? Is the valve spring weakened or a dead o-ring perhaps? I can order a new valve but I'd like to try to fix it myself.

Remove the valve and inspect the orings for damage, sometimes they can be salvaged

Is there a space for an allen key beside the fill valve? try tightening that if there is.

It's not the fill valve, it's the flow valve.

-Edit, replaced the valve and did maintenance on all my other ones and they are all working better than before. Just had to completely remove them from the mag and work in silicone oil into all the valve parts.