there are a few things going on. the design was to bottom the shock and arm at the same time. When everything is new, this happens. as the bushings age, almost imediately, it makes the shock bottom out way after the arm bottoms and bends around the bumpers. This also happens when the shock rubber gets smashed out of the shock. Also, the shock preload is held against the limiter straps bending the arm the other way when not compressed. This combined with a thin arm material, and many, many undercut welds at this flexing point causes the problems.
best case fix,
bearings or tight bushings in shocks
tightened bushings in w arm, add grease fittings to lower mount
keep bumpers in w arm to take load off shock bumper
reweld cracks and slide a solid piece up through the inside of the W arm tube and spotweld a couple times on each end.
It will last for ever.