Off duty TC reported rear M1 car B4 doorfailed to open at AMK SB. Staff TAP checked and feedback no abnormality found. Staff (RFP) checked on the NB and feedba ck no abnormality found. ~~~~~ 1615 Off duty TC reported B4 door failed to open at AMK SB. Staff TAP checked and feedback no  abnormality found. Staff(RFP) checked on the NB and feedback no abnormality found. CE checked: 1615 B4 Door Slow in opening.  1615 B4 door RHS roller found damaged & LHS roller - OK. Replaced the RHS roller & cleaned J-rail/guide rail - OK. Function test door operation - OK, no DIR lit up.  Alan/Lee PT/Anand/Kamarul 45122