My odo/trip assembly just failed as well (1997 850 w/ 112K mi). Best price found on the part was $179, but nobody could verify that was the problem. The tripmeter wheels turned freely (when removed) and all other gauges work fine. My local shop (specialized in Euro cars but not a dealership) sent it out for diag & repair for an estimated $220, so I opted for that to ensure it's fixed and not get stuck with an expensive, non-returnable part.