what i ALWAYS use to separate the retaining ring from the case is this snap back watch case opener AND a watch makers hammer tape around the case as much as possible using electrical tape, turn the case on its side, insert the sharp edge of the opener between the ring and the case and gently tap with the small hammer, work your way around the case and it comes off, unwarped and no case damage as long as you tape it up a bit. to press crystals this is my preferred method. cheap and very effective 1 1/2" polyester adapter from home depot with a flat nylon disc in a taped up bench vise, turn slowly and press, keep it straight. just make sure the crystal isnt too tight for the case beforehand, or it will crack and you may not even notice