No idea. Just started the annual today and my mechanic said I need to replace them. Exact message was that the aft was cracked and the fwd is "loose" and that both needed to be replaced.
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.
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