[MrForbes]

I would expect that arm to bend there....it is very weak. Even though it started out as 1" square tubing, it isn't square tubing now, because of the slots cut in it, presumably for weight reduction. And it probably should have been 1.5" or 2" tubing in the first place. A small increase in tubing size gives a big increase in strength.

A quick fix could be made by straightening the arm, then riveting two pieces of 1" angle over it, one on either side.