How do I get into my 1998Ford Transit van when key won't unlock?

How do I gain entry when my key(which locked the doors)won't engage the unlock mechanism,jamming at the 2o'clock position(or the 10o'clock position for the locks which work the other way round)?I have thoroughly WD40'd the locks and left it to penetrate for over 24hours and wiggled the key in all the lock barrels extensively.Do I have to destroy the mechanism?(Levering off a lock cover and getting-to with a hefty screwdriver,for instance;or do I have to drill out the barrels down the key axis,and what size bit is most effective?),or what do I do,short of distorting the door/frame or breaking a quarter-light?