I've struggled with a stiff door lock for weeks, and though some git might have tried to super glue me!! I tried a squirt of WD40 penetrating oil in the lock key hole with no success, so started to take the door card off, but failed as I couldn't get the window winder handle out. So I eased off the inner window seal on the door capping and gave the lock mechanism a long squirt from every angle with WD40 using the directional tube. It must have knocked off the dust and lubricated everything, like new again!! A 5 minute fix - must do the passenger door as a preventative tomorrow. Cheaper than a broken key in the lock.