If it broke that easy I suspect it may have already been loose and had some play in the fasteners. I've seen pics of a few that were caught before they came completely unglued. I'd advice anyone with a pre-18 machine to check the pinion as a regular part of maintenance if they aren't gonna replace the cover. If one or more of the bolts are found loose, put a drop of blue loctite on the threads and torque to spec.
The above might not prevent the failure but it sure couldn't hurt to try to catch it BEFORE it explodes.