A sealing structure for a gas turbine engine includes a rotor that has a rim with slots and a cooling passage. The rotor is rotatable about an axis. First and second blades are arranged in the slots and respectively including first and second shelves facing one another within a pocket that is in fluid communication with the cooling passage. The first and second shelves form an opening. A reversible seal is arranged within the pocket and has a body that is configured for operative association with the first and second blades in any of four orientations to seal the opening in a second condition. The seal includes first and second protrusions respectively extending from first and second faces opposing one another. The first protrusions supported on the rim in a first condition.