I tend to think it got seriously dropped at one time (or seriously abused) to produce the damage you describe. I'd check with the factory about possible frame replacement first. If frames are available you can get a cost estimate. Then you can check to see if a weld repair is possible and what it would cost. Given the nature of the material, location and possible machining to clean up the area, a few extra bucks for a frame would probably be a wise investment.