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Originally Posted by Adam
I think you are referring to the porous cases that affected some early boxsters. The RMS IMS failures aren't a result of a casting flaw. The RMS usually occurs because the crankshaft is not supported sufficiently and it distorts the seal causing oil to blow by. I believe IMS failure can happen a couple different ways, but these are due to design flaws in the m96 engine not casting flaws. These flaws were not completely fixed on the 987 series cars either.
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The 986/996 engine blocks are cast without machining to Center-Bore the Crank Opening. This results in varying center bore tolerances in which the crankshaft is not supported well. This will cause the crank to rub disproportionately on one side of the seal leading to it's premature failure.
You can also add porous engine cases to the list of flaws
