That looks like a slightly different revision of the RAM ball mount that I have on my CT125 for a Garmin Zumo XT.
First I followed the provided instructions and mounted it to the front brake reservoir base:
I was not happy with that pass-through setup. The washers provided for it were too small so when I tightened the bolts they started sinking into the cheap metal. I believe the spacers for behind it may have been plastic as I recall not trusting them to not give way as I tried to achieve an appropriate clamping force to just keep the master cylinder from drooping. I scrapped that idea and ended up moving the RAM mount over to a Barkbuster clamp instead. Added some larger washers, and it fit well enough that the spacers behind the mount could be eliminated.
I haven't had any issues with that attachment setup yet, but I imagine that if it were to hit anything the cheap metal would break same as yours did. If I didn't find my handlebar bag extremely convenient I would probably switch to one of the handlebar top clamp RAM mounts instead.
Does the Montana 700i plug into a cable that's in the bracket, or are there pins permanently attached to the bracket? The Zumo XT bracket has a cable fed up into it, sandwiched between two plates, and screwed in place. Since it's a cable, it's flexible. Mine occasionally loses power on every motorcycle I've had it on, and the quick fix to restore power is jiggling the cable that feeds into it.