Oil Questions

[Nicholas Menaker <72074.2716@CompuServe.COM>]

I have an 86 4KCSQ.  A little while ago, I checked the list about what to add in
the tranny and diff in the rear, as to new oil change.  It has NEVER been done,
car has 150K+  The general tone was to put Mobil 1 75W-90 in BOTH places.
Manual Tranny and the rear diff.  Now, the oil is only one rating, GL-5, or
GL-4, I am not sure which.  Someone JUST wrote today, that the more "slippery"
oil in the TRANNY was actually bad.  Too slippery and grinding of gears would
occur.  Is this correct?  Has anyone put the SAME Mobil 1 75W-90 in indeed both
places?
Love to hear some answers before i do this on Wednesday.

I thought I heard that AUDI had decided to put Synthetic oil in BOTH places as
well, as of say 87 or 88

Nick out