They crack due mainly to vibration. If you are careful to mount exhaust properly, and keep the mounting bolts tight I doubt you will have any problems. As to that hole, if it was my bike I would simply dent the damaged area in a little to provide more clearance, roughen and clean with acetone, then JB weld it. Its pretty difficult to TIG weld used exhausts nicely, as oil/crud tends to get drawn into the weld area, which makes a good job less than easy. For non stress repair, I think you would be much better off with JB weld. Both exhaust boxes on the SY tend to get get blocked with unburnt oil relatively quickly, and its a good idea to find a good full synthetic oil and run this at 80:1, which will greatly reduce the speed at which the boxes get clogged. Later bikes had a modified middle box, which improved performance quite a bit, as the earlier one seemed quite restrictive. The UK Scorpa importer built his own bikes based on the TY Yam motor used in the Scorpa, and found that carefully designed and made intake and exhaust systems, meant performance that was quite a bit better than the production machines.