Punto (Mk2/2b) Repair a Door Lock

[ame]https://youtu.be/yf4ZVu-zk0U[/ame]

Hi mate! Thanks for the detailed walkthrough... My Punto MK2 of the year 2000, has started to be cranky about unlocking...
It has central locking and electric windows. I can lock it perfectly and smoothly from any of the doors, but when I try unlocking it from the driver's door (Left Hand drive) it is really hard and doesnt work well.. What should I do?? New Lock? Or just apply some WD-40...
I eagerly await advice. Thank you