I think the spring only applies to the disco 1
I have had to replace all 4 now on mine. It's not that hard, allow about an hour. You will need some torx bits as well (the star shaped ones) so make sure you have some before you start.
The reason it's failing is because the lock has 2 motors. The superlock and the normal one. The normal one has failed so on locking with the remote it's superlocking which forces a lock, but unlocking only removes the superlock and the second (faulty) motor does the unlocking. You can verify this by trying to lock with the button on the dash. You will see that does not lock the door.