Remove the sight, turn it upside down and place on a steel support like a vise jaw. Use a center punch to carefully put a couple of dimples on each side of the underside of the sights "wings." Trial fit it in the dovetail. If it has enough resistance, apply red loctite to cleaned surfaces and assemble. If the sight is not quite tight enough when you trial fit, add another dimple to each side and try again. There should be good resistance when the sight is inserted 1/3 to 1/2 way into the dovetail.
Do not dimple the dovetail channel on the slide! Only the bottom of the sight "wings."
On final assembly, use a caliper to insure the sight is centered. It will be very difficult to remove after the red loctite has cured.