Hello I'm Chris a Certified Engine/Transmission Specialist.
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Sounds like the trans will need to be overhauled and shaft bearings replaced as well as the 5th driven gear and synchro. The synchro may be fine though since they normally create no noise once engaged.
BMW Technician
Specialized Tech. in Transmission, Transfer Case, Driveline, Brakes, Engine, Elect.,and Suspension