Rear M1 train doors not proven closed. TC opened and closed train doors few times to no avail. Pax w as disembarked. DIRBS was operated and train withdraw back t o depot. ~~~~~ Depot found 1624 B1 door solenoid plunger C-clip dislodged and obstructed door locking motion, resulting in door not proven close. C-clip replaced & door cyclic tested ok. Train released on 30/01/2020. L3   #1624-B1 door solenoid plunger C-clip snapped obstructing vertical slide operation.Removed damaged C-clip and replaced ok.Checked J-rail and door guide rail for F.O.D ok. Carried out door cyclic test and ensured door lock s/w positive engagement ok. Done by Johua. 30/01/20