The first question I would ask myself is whether the top lever return spring is weak or cracked. Does the bolting become tighter if you push the top lever toward the left, without excessive force, of course.
My only crossbolt guns both have a compensating adjustment screw that limits the travel of the crossbolt, which has a very slight taper. Backing this screw out a bit permits the bolt to move very slightly more to the right.
These are a couple things to check before you start thinking about TIG welding the hole in the rib extension, or adding weld to the bolt and re-fitting, or machining a slightly larger bolt.
I know you do not want to hear this, but this may not be a DIY project. Always be willing to know and admit your limitations. And remember that sometimes, you just can't beat a bricklayer at his trade.
