Your mechanic should know that there are some (needless to say) very expensive shims that go between the prop and the front bulkhead so that it is not "loose". If it was not installed properly and is in fact "loose", that is likely the cause of the cracked rear bulkhead as this would allow the spinner to "wobble" stressing the rear bulkhead.
Good point, Bruce, I'll be sure to ask. My mechanic is a former 150 owner so he knows the model well, but I'll be sure to remind him about the shims before I purchase another forward bulkhead.
-Jim
