Waaa? 3/8" bolts mounted from one side in a steering system?

That don't sound right.

The Briggs use a ton of 3/8 hardware and have no problem.

Also, any 3/8 bolts should be 24 not 16.

Better pics of the part before it broke?

EDIT: I went back looked at your earlier pics of the swingset. that's not a good design. Can you run a bar across from bolt to bolt? The shank of the bolt should also extend into the support section(or all the way through), not threads right at the stress point.

one more option would be to weld a piece of angle onto the back of the tube clamp with a hole in the top for the bolt, you would of course have to clearance for the tube. just pitching ideas.
Is Emanuel working with you on the solution?