I am not going after anyone. I am just gathering opinions on what possible causes might be, The crack idea also seems plausible.
We are turning it into insurance.
And letting other 182 operators know where to look during inspections.

Hmmm...from an engineering perspective I wonder if installation of the SPW kit results in loads being transmitted/absorbed in other places? I'd love to know if the new tunnel part dropped right in or is the structure surrounding the tunnel distorted in any way? The engineer in me would also like to look at the tunnel with a video camera on the water...transitioning to airborne...landing...etc...to watch what happens. Or be able to measure it in those different phases of flight. Big $$ to do a study like that though. Unfortunately I don't think a sandwich 'patch' repair of a structural area like that would be allowed. Good catch by the maintenance crew on that one, although the damage is obvious. Sometimes folks just don't pop those panels off and really look around. Sucks from the $$ perspective but what if it got worse and the tunnel let-go during a water landing or something bad? Unfortunately, without knowing the cause there is that possibility of seeing that same condition again if there is something amiss with your float set-up, which I HOPE isn't the case.