The leak is caused by a damaged poppet.
Depending on the age of your gun you will have a white plastic poppet or the stainless version with rebuildable head fitted with either dura 70 (older) or dura 90 buna 0 ring fitted.
The 90 is harder wearing and will last longer than the 70.
If its a plastic poppet, swap it out an get a SS lp poppet, if it already has one change both the 0 rings.
That will stop your leak.