TC reported cab door unable to secure. Subsequently TC managed to secure the cab door in closed posi tion. ~~~~~ [Level 3] [NSEWL] T409(3627) B-side Cab Dr Unable to Close at CBR SB: TC was unable to close B-side cab door. Pax disembarked at CBR SB. DIRBS operated to proceed. LTOC informed. (sent at 08:48 21-May-2024) CE:3627 B/S cab unable to closed fully L3 In depot, fault was able to be duplicated with the cab door not fully closed, leaving a gap of 20mm. Found the top roller guide sunken down, with mounting screw loose, hampering the movement of the door roller and causing the cab door to be stuck while closing. * Realigned top roller guide rail and cleaned guide rail.    * Cycled 3627 B-side cab door 30x; no abnormalities observed, DMI & DIR able to light and extinguish accordingly. * Checked all cab doors preventively, open/close speed and operation ok. * Checked no FOD on guide rail at cab doors. * Resealed DIRBS. Done by Rizman/koh/Sanip 45433