What was found
FLT#683, BOS-RDU. (AIRCRAFT PERFORMED AN AIR TURN BACK TO BOS). 'L ENGINE FAULT 75 L ENGINE FAULT - BAV INOP; REMOVED AND REPLACED ENG #1 BUFFER AIR VALVE SEE LP 4092257, ITEM 1 (PERFORMED IDLE LEAK CHECK OF BUFFER AIR VALVE PER AMP 71-00-00). A/C OK FOR SERVICE, NO FAULT. '