Not knowing how adventurous you are, you may want to try and replace one part at a time and see if your problem goes away. I would replace the sear spring first as they can lose their tension after being in place for untold number of years. If that doesn't take care of the problem you can move onto the sear or cocking rod. By doing this you can isolate the offending part quite easily and learn a little more about your rifle.
Rick