Just taken the catch to my engineer friend and his thoughts are..
The rod is broken off in plunger and are of 2 different metals.. the plunger being the softer metal.
In his view you cannot braze these 2 parts together. The manufacturing of these parts looks as if the plunger was probably moulded/cast on the end of the rod and in this case the rod has broken half way into the recess.
This is not easy to repair as my friend is going to drill out the rest of the broken rod and if that is successful look at ways such as remanufacturing a new rod. In my view I think these get broken by not retracting the catches whilst fitting the targa covers to the car.