The screw would have no affect on the safeties malfunction. On an unmodified Lefever 3-position safety, safe is in the middle. When pushed forward to fire it will be an auto-safe & returned to safe on opening. As mentioned though the safety is actually pushed beyond safe to the rear fire position. There is a flat spring under the safety with a little roller on the end. In the rear position this roller rides up an inclined ramp & upon the lever returning to center the sprong pressure causes it to roll back down the ramp to safe. The purpose of the screw is for times as trap etc, where the auto safe is not desired with the safety pused to rear fire position the screw can be turned in & lock the safety in this position. This it does by having a small pin projection on end of screw which enter a hole in the safety slide. As I mention make certain the safety is in fact returning fully to it's proper position. Gunk build up in the track or the roller could be stopping it before reaching it's actual detent. Just after closing the gun simply push forward on the safety a bit & see if it moves & then hits the detent causing more resistence to further moving. If it passes this test then you likely have a problem with the trigger itself, though the block could be worn or bent. One simply has to examine all parts/possibilities to say for certain.
