Try heating the stuck locking mechanism with a hairdryer on high heat setting. A drop or two(use very little)of penetrating oil may help if used at the same time, the heat will help draw the oil into the threads. Do not try to force the lock, wiggle it back and forth, as much as it will allow. Never use any tools other than your hand, at most use a rubber pad for better grip. I have rubber strap wrenches, they have a pinch point that will deform whatever they are pried against.