[MadMax]

well, don't forget:

-after cracking, poorly supported spring guide would have broken easily
-do some fatigue surface analysis to determine if breaking mechbox is cause of spring guide failure or spring guide is cause of mechbox failure (differentiate cause-effect)
-without fatigue failure analysis, all we can do is pull ideas out of our ass

One thing comes to mind: If the spring guide failed well before the mechbox (SG failure is cause of mechbox failure), then there should be some significant evidence of wearing on inside of the fallen off chunk of mechbox. Very heavy cyclic scratching on the broken off bit would indicate that it was bearing hard against the damaged SG for many cycles before it broke off. If there is little evidence of cyclic wear, then the SG was not scrubbing the busted off piece before it broke off. Therefore, the SG could not have been loose before the piece broke free.

i.e.: if the when the piece falls off, there can be no significant force between the SG and the inside of the busted piece. Therefore the evidence or lack thereof of heavy scratching would indicate if heavy uneven bearing forces were bourne by the piece before it failed thereby indicating what failed first (SG or mechbox)