I have an idea to solve the whole broken motor mount debacle! Click the image at right for a fully realised back-of-envelope plan, but basically it amounts to the following:
The motor mount is usually fixed by two screws to the existing motor mount stick. This allows for zero movement (a Good Thing), but also has zero ‘give’ so any prop-strikes tend to cause the mount to break. My crafty plan is to use only one screw to fasten the motor mount, and use rubber bands (or o-rings or something elastic and sturdy) to fix the other end of the mount. This way, the bands should keep the motor mount in place during flight, but allow it to pivot downwards if (when!) the bottom of prop is forced backwards (e.g. when it strikes the ground while the model is moving forward).
Obviously the plan is to not have prop-strikes at all, but when they do happen, I’m hoping this solution will work! This all relies on the rubber bands being strong enough to take the pull from the prop without moving, but soft enough to ‘give’ more than the aluminium mount. I think a selection of different rubber bands and some benchtop experimentation should result in a working solution.