TC reported smoke external Rear M1. Staff (BGB) checked and confirmed no sign of smoke or fire and n o abnormalities. Rear Train 407 and 240 line clear and repor ted no abnormalities. ~~~~~ TC reported smoke external Rear M1. Staf     Check Tims found FC-721,Further check found external smoke detector water seepage into PCB.Replace smoke detector and function test ok. Smoke Detector- Old s/n:   New s/n: SD-018 Done by Koh/Faddzal. 25/08/21