Many times in such cases there has been a change or update to improve something so they make you buy the whole unit. A good example was the oil filter adapter plate O-ring for the E30 was not available separately and you had to buy the whole adapter plate with new O-ring but the reason was that the O-ring groove in the replacement was machined to provide a little more crush on the O-ring to keep it from leaking again. I think it was just a case of poor engineering specs or maybe O-ring material or spec not matching the groove. Gleaner combines had exactly the same problem with their hydraulic filter block. I wouldn't be surprised if the new bearing/housing was somehow different. Was the original bearing not a sealed unit ??

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)