this is the method my well seasoned Godfather the watch maker uses and it never fails, and never damages a caseback. he utilizes this on most stubborn and soft gold cased rolexes and was trained by rolex manila decades ago to use this method so as to minimize any chance of damage. it also works equally well on any steel cased watch.
use 2-part epoxy and affix a suitable tool bit to the caseback. use a tool on the tool bit to unscrew the caseback while the watch case is held in a suitable holder with wood or plastic insulators. after the caseback is removed, simply soak the caseback and epoxied tool bit in solvent to dissolve the epoxy.
hope this tip can help some here who are afraid of damaging a valuable case and caseback.