When you install something and tighten it to 50-55 lb ft, that doesn't mean you can get it out years later by applying 50-55 lb ft in the opposite direction. It may be more, it may be less, but if it hasn't come loose, it will probably be more, due to micro-corrosion in the thread. And by my standards, 50-55 lb ft is outside the proper range for 3/8" drive sockets. It is not a problem of shearing the drive, it is an issue of bearing pressure on the four corners of the coupling. The squares can be mashed slightly.
