Train doors at Front Dt car were not proven closed. TC recycled train doors a few times - ok. Staff( WDL) checked and confirmed no train doors abnormalities. Tra in doors at Front Dt car were not proven closed. TC recycled ~~~~~ 2502 One of the train doors was not proven closed. L3 TC recycled train doors a few times - ok. Staff(WDL) checked and confirmed no train doors abnormalities. L3 2502 Fault unable to be duplicated in depot. From ER, TC cycled doors x3 times to clear fault. Fault did not recur afterwards and train continued running on ML until scheduled withdrawal. Back at depot, doors were able to cycle without any abnormalities. Postulate FOD dislodged when doors were cycled. Side finding: Found #2502 A4 LHS inner roller pitted. Replaced roller. Cycled doors 20x, found no abnormalities.    Door operation was smooth without wobbling. Checked and ensure guide rail is free of any FOD. Preventively serviced both J-Rail and guide rail. Door static test û door open/close speed SATIS. Door manual force check û ok. Check EMV for any residue voltage when door close û ok. Function check door operation û SATIS.  Shaun Lau 45488