I'm working on this same problem right now for a friend. As others have said, clean it, then replace the spring. You can get them lots of places; I got mine at PTG.
Also in this case, someone in the past had replaced the firing pin with a "lighter weight" fluted firing pin. So I ordered both the spring and the standard steel firing pin. After doing that, I also discovered that the cocking ramp on the bolt body was either worn out or someone had ground it, so the angle was steeper and, especially with the new stronger spring, it wanted to catch and try to bend the cocking piece. So I ended up getting a whole new bolt. So check that bolt body before ordering the parts, so you can get everything you need the first time, instead of 2 orders, like i had to do.
And I recommend always storing your guns with the hammer or striker down, not cocked.
Here's a pic of the bolt, with a new bolt for comparison.
Also in this case, someone in the past had replaced the firing pin with a "lighter weight" fluted firing pin. So I ordered both the spring and the standard steel firing pin. After doing that, I also discovered that the cocking ramp on the bolt body was either worn out or someone had ground it, so the angle was steeper and, especially with the new stronger spring, it wanted to catch and try to bend the cocking piece. So I ended up getting a whole new bolt. So check that bolt body before ordering the parts, so you can get everything you need the first time, instead of 2 orders, like i had to do.
And I recommend always storing your guns with the hammer or striker down, not cocked.
Here's a pic of the bolt, with a new bolt for comparison.