Just my 2c's. When I replaced the turbo on my 2003 E39 530d about 3 years ago I had to provide Turbo Direct with my turbo's serial number as they said they needed it to be able to supply me with the correct turbo. Mine was making a howling noise when driving slowly and at speed it was difficult to determine if there was any difference in noise due to tire roar, wind noise, etc. Mine had a very small piece of exhaust vane that had broken off but I could feel no vibrations. The car certainly did not have any less power that I could determine. I opened the turbo after I had removed it and the bearing was perfect with no discernable movement or wear that I could see.
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If only you had answered to my threads sooner, I would have known exactly what had happened and what I needed to do. Almost 2 years ago.
Anyways. I have a new turbo now which will be fitted on Monday. It's an original Garrett GT2556V which I picked up for 8900.00 brand new with warranty.