Grinding in the Rear?

["Teel, Eric" <teel@xxxxxxxxxxxxxxx>]

Hello Gentleman,

My cousin in Sacramento has a 1988 528e which is now giving her some strange
problems.  First, the car has a rattling noise while driving at low speeds,
i.e. street driving, and has a grinding noise at highway driving speeds.
Now she took to car to a local jack of all trades shop and they told her
there was GREEN fluid in her rear differential and it needs to be rebuilt.
Green?  Is that possible?  Isn't gear lube black and trans fluid red?

If anyone has an idea where she can take the car for a respected Bavarian
inspection please let me know.  Also, if there are any parts dealers that I
can look into getting her a rebuilt or used rear differential if needed.  I
really liked the car and I would hate for her to get rid of it because of an
ambitious shop trying to make a killing on an unknowing woman.

Thanks.

Eric 
'94 318i (Daddy's toy looking to upgrade to V6 or bigger!)
and still looking at the 
'84 633csi  -> restorable commuter for the weekends
'86 735i -> project car and possible replacement commuter for the E36

PS: 
Any information on the pro's and con's of getting a '84 633 csi or '86 735i
would be appreciated  (teel@domain.elided)

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