May not even need work on the trigger. There is a small spring underneath the top tang that gives the safety slide a bit of tension and provides a small bump for the safety slide to stay in place. The screw holding this spring may have loosened and no longer holding the slide in place. If this should be the problem it will be a one minute fix once the stock is removed. I had this happen once on a nice A&D actioned gun.

When an old man dies a library burns to the ground. (Old African proverb)