Bap,
That is actually a fairly simple fix. You will need a small punch and a brass hammer. You just dimple the steel on one side of the dovetail with the punch, insert the sight into the groove, then dimple the other side with with the punch and this should hold it in place. If you don't understand what to do or you don't feel comfortable doing this just take your gun into a trust worth gunsmith and it shouldn't cost you much and it is a fast fix. Don't ruin your collectors item gun though because others may not understand the personal value you place on this or any other weapon. Guns are only worth what you are willing to pay for them and if you are willing to pay for a 1 of 500 gun then it is obviously worth it to you to not use it if you don't want to.
Navylawdog