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It is a mix of issues IMO, it is caused by the following:
1. The dual mass flywheel is heavy, and hanging off the back of the block, which creates a lever effect on the crankshaft
2: The engine is of modular construction - the crankshaft is in its own bearing cradle, which is then bolted into the case. The earlier 911 as well as the GT-2, GT-3, and turbo have the bearing journals machined directly into the case, ensuring all of the bearing bores are concentric. In the newer motors, the front and rear bores are in the case, and the rest of the bores are bolted in. I feel that this can introduce slight errors in the alignment of all of the bores, making the problem worse.
As of last count, there are about seven revisions to the RMS and installation procedure for both boxster and 996. If the case if too far out of alignment, the engine needs to be replaced.
AFJ
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