This is a common problem on W124's, which often results from someone attempting to pry the panel off rather than pull it upward.

Armrests are available separately. I'd try using some epoxy to repair the hooks first. Also, the plastic dowel fasteners (looking from the rear of the panel, they look like plastic rivets) are heat/press molded and tend to break away from the door panel. Drill into the center of each, and fasten with a screw and washer.