You can go to any hardware store and pick up a set of ez outs. They are drill bits that when spun in revers cut into the bolt remains and unscrew it. Your alternative to this is to drill and tap it, but trust me the ez outs are cheaper and you can always tap it out if ez outs don't work. Hope this helps with the bolt issue, and if the weld keeps breaking then there is potentially something else wrong. Ask yourself why the stress is being added to that part to make it break, perhaps something is not working properly. I don't know for sure, I am new, but that is what comes to mind.