A few months ago the bathtub plunger lever was stuck/rusted open. I got the lever moving and then the plunger became unhooked and the drain was permanently closed. I removed the lever from the bathtub wall, and fished the bars to reconnect the hook that unplugs the drain. However, if I move the lever the plunger drops and blocks the drain and I again have to "fiddle" with the lever until it hooks the drain plunger and pray that it stays open.

How do I fix this permanently so that the lever is reattached and I can use the tub plunger lever the way it should be used. Do I have to call a plumber to replace the plunger and lever mechanism?