[thstone]

The CORRECT answer is: Only you can decide.

I replaced my clutch at 92,000 miles and did not replace the original IMSB. At 107,000 everthing is still running fine. Its my daily driver and I go to the track all of the time so the car is driven often and hard.

No one can explain why some IMS bearings fail early and some seem to last forever, hence only you can determine your level of comfort and risk.

The odds are debatable but certainly 90% of engines never have an IMSB issue. Those are pretty good odds. But if you're in the percentage that does have a failure and you don't have the money to replace your engine, then it can be a true heartache (especially if you paid top dollar for your car).

I view the M96 engine as disposable and the super low purchase price of my car ($10K) reflected that reality. When the engine blows (from any of the 20 or so known engine failure mechanisms), I'll replace it with another engine and still be ahead of the Porsche owners game financially.

If you're worried about it and/or can't afford a replacement engine ($5K-$8K), then definitely replace the IMSB. You'll feel better and have more fun with the car knowing that you've done what you can to prevent the engine from exploding. But if you ok with the odds and don't worry about it and/or can afford a replacement engine, then take a pass on the bearing replacement and use the money for something else.