I recently cracked the handle on my little jackhammer. It was an easy fix with some two part epoxy.
First I removed the screws holding the handle together and removed the broken side grip.
Here you can see the crack. I had gotten the jackhammer stuck and decided to try to pry it out – wrong!
Use some regular two part epoxy and then wrap it with an elastic or some dental floss to hold the part together while the epoxy cures.