Check the breech seal but probably the piston seal and/or spring. You'll need a special tool in order to remove the trigger assembly and get to those. @KWK Knows much more than I do about that gun though
I thinkhe's decided to get something new. Probably a good idea. He just shoots small yard varmits. I had an old Diana that was a good shooter but sold it to my brother. He about poop when he saw the different choices you now have and the price ranges. lol