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I read the SKF bearing book on bearing design from cover to cover and bearings have a tendency to fail unpredictably if not operated within their original design specifications. The IMS bearing is of the deep groove design and is designed to be grease lubricated not oil lubricated. If the seals fail or are removed the bearing isn't correctly lubricated and service life becomes unpredictable. The later model m97 engines in the 987 from 2006 used a larger diameter bearing ( so turn slower) than the earlier m96 so the crank case is a different design and they cannot be retro fitted without machining. Personally I think there is no discussion, fit the LN bearing wherever possible , it's not only specified for oil lubrication , it's also better at higher temps. It is not however without it's limitations , as it has lower load ratings and speed ratings than the oem unit , hence the hesitance to stipulate it's 100% guaranteed.
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