Had one on the bench here in very distressed state a few days ago. Working quite well now.
Worth checking muzzle energy around 65/70 bar then 100 and again at 150.
Reg is usually around the low figure so if energy drops off at higher levels it's defective.
Interesting hammer adjustment as found

https://photos.app.goo.gl/aSS36Mf4hMwXQPfUA