I would try the primer under the strain screw first. And if that works, I'd order a new mainspring. They're cheap, and easy to replace. Require no fitting, just remove, and replace. However, if you like that easy trigger, it'll probably be significantly harder with a factory spring. So I'd consider an aftermarket reduced power spring. Personally, I have trouble believing that's the problem, because you've said that it's only a part time problem. I'd think a weak spring would be always weak. But the spring is the easiest to check, so I'd certainly start there.