My E39 has 305,000 Km and runs strong. I use:
-Brake Fluid: ATE SL.6 (this is the low viscosity version)
-Manual Tranny: Tried Red Line MTL, and Royal Purple. No good, the shifts were "crunchy"
Pentosin MTF-2 (designed for ZF and Getrag) http://www.pentosin.net/specsheets/Pentosin_MTF-2.pdf
BMW bulk at Budd's @ $35 / liter.
For the diff, any synthetic GL-5 in the correct weight will do.