Hey dude I did the exact same damage to my front mount. What I did was file away the damage and filed the bottoms of both mounts so they are flat and even. I probably took nearly 10mm of material out. I then drilled the bolt holes deeper into the casting (not heaps!) and retapped the holes. Its not a pretty solution but it seems to have worked for me and hasn't failed again since. This pic shows the damaged side, the other side I filed down to match but obviously the bolt is fully enclosed on that side.