Try to get those bolts out of the case first.
Then if the case isn't stripped get some m6x1.0 high grade bolts (think its like grade 5 or grade 8.8) and bolt it up!
If there stripped then get some 1/4 bolts (same length) and just carefully tighten them in there. Should make it a lot stronger.
And the reason they failed was becuase the motor mount isn't flush with the adapter. So loosen the rear bolts and adjust the motor flush.
Hope this helps!