Typically, bearings fail because the seal fails. The seal is a wear item. If the bearing looks good, repack it with new seals. Most of the other bearing failures are due to poor practices when servicing a bearing, such as letting dirt in, improper preload, and damaging the seal or not seating it square. It doesn't take much to shorten the life of a bearing. One must be nothing less than perfect when servicing a bearing.

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95 E320 Cabriolet, 169K