What was found
DURING CLIMB AND PASSING FL 180, RECEIVED A RT THRUST REVERSER UNLOCK LIGHT AND THE ASSOCIATED CREW ALERT SYS WARNING MESSAGE. REDUCED RT ENGINE POWER TO IDLE AT WHICH TIME ALL WARNINGS EXTINGUISHED. FOLLOWED AUTOMATIC CHECKLIST FOR THE THRUST REVERSER UNLOCKED CONDITION, AND ELECTED TO RETURN TO THE DEPARTURE. LANDING UNEVENTFUL. MX LOCKED DEFECTIVE THRUST REVERSER AND ACFT RETURNED TO HOME BASE SUSPECT WORN BUSHINGS ON THRUST REVERSER DOOR BELLCRANK PN: 1159PM41550-55 WHICH MAY HAVE CAUSED THE DOOR OR DOORS TO CREEP SLIGHTLY TOWARD THE OPEN POSITION ENOUGH TO ACTIVATE THE UNLOCKED WARNING SYS.