My daughters KA has a very sticky drivers door lock. Tried a gallon of WD40 but it is still very graunchy, to the extent that she now locks the car from the passenger side. Any ideas on remedy or how to remove the lock to try and lubricate it internally?

I've had the door card off, but I cannot seem to suss out how to remove the security shroud that covers the lock mechanism.

By the way, it's manual locking, not central locking, a very base model!!