2005 SEAT Ibiza door locking problems SEAT Ibiza

Hi, I am having problems with the locking on a 2005 Seat Ibiza. The drivers door opens and locks as normal, but I am having trouble with the other 3 doors, especially left rear. Generally after a couple of minutes of messing around pressing lock/ unlock it locks fine. In the last couple of weeks though the left rear door has taken longer to lock, sometimes having to be left unlocked over night. Does anyone have any ideas about resetting the locking or any other solution? Thanks.