Tranny and Diff Oil recommendations?

["Martin Stanczak" <martin@xxxxxxxxxxxxxxxx>]

I have changed the diff oil in my E36 during my previous Inspection II to
Castrol Syntec 75W90 oil.  Since then I have noticed that there is a very
slight whine from the rear diff when coasting. The car has only 55K miles on
it so I think the diff should still be in perfect condition.  With another
Inspection II coming up this summer, I am wondering if I should use a
different brand of diff oil, or maybe just use the BMW oil from the dealer?
My other question is about the manual tranny oil.  My service manual says it
should be changed every other Inspection II, therefore it is due for a change
this time around.  Any recommendations?  I have used Mobil1 75W90 in my
previous car, however I had to drain it because I could not shift gears once
the temperature dropped significantly below freezing.  I know BMW recommends
Dexron II Automatic Trans Fluid for their manual transmissions, would it be
wise to go with a brand name synthetic Auto Tranny Fluid or just stick with
the dealer oil which is especially pricey here ($20/qt)?  Your experiences and
recommendations would be very appreciated.
Thank you for your responses to my question about a whining sound from the
belt pulleys - it turned out to be just a blown bearing on the A/C belt
tensioner.
Martin
'95 318Ti
'87 MR2

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