Scary - RK bolts broke

I had been hearing some clanks on bumps for a few weeks. Checked all of the sidecar attachments by eye (not wrench). Today it got really noticeable and when I stopped I found this.

The two bolts holding the TLE rear mounting bracket to the RK frame had snapped! Anyone had this happen? (at the bottom of the photo you can see the hole where the remains of the bolt exist).

I'll try to get the remains out - not sure how difficult that's going to be. Should the repair be extra hard bolts or two welds?