I use SWEPCO 201 80W-90 in our limited-slip diff.
Wears better than Mobil 1.
The Porsche Club swears by it, esp. for MB tranny's (928 automatic used a MB tranny).
I track both cars, and my mechanic who races Subarus and Pro-Spec 7's has been converted as well.
1988 360TE AMG