. . . to the point of failure is not covered by warranty. No way. Service technicians use only light torque combined with a tiny droplet of Loctite. It's also really rare to encounter a defective screw bar of any kind. Has to happen sometime though, so maybe you just had the bad luck of that draw. Then again, an experienced watchmaker can use a very small carbide bit with a modified tip (with the watch case protected/padded and mounted in a stand) from the outside of the lug to bite into the broken piece and screw it out. Note that to effectively clamp a case in position for such a procedure, everything has to be removed - stem, crown guard, movement and crystal. However, note that if your service technician already tried that and it didn't work, it's most likely that you torqued it into position so hard that the threads locked. If your service technician looked at it and immediately suspected locked threads, he may not even have bothered to try because there's a danger of doing further damage to the case and lug during the procedure. If there are locked threads in a steel or ceramic lug, the lug (and often the case too) is ruined.