I just acquired a vintage Elgin wrist watch, it`s an automatic with a waterproof case, and I need to open the case to inspect the movement. Got out my case wrench and started to try to unscrew the back, and it will not budge. It actually sheared off the corners of the inserts for the wrench! Does anyone have any suggestions for opening a waterproof case back like this? I've opened cases that were stubborn to get started, to change batteries, before but this is just not moving at all... Help, please?