Per the BMW TIS:
(USA) E9x N52 engines ('06-325i/330i, 328i,) rear diff is designated 188L/188LW and takes SAF-X0 (75w-90) with a 1 liter fill.
(USA) E9X N54 TT engine [and the M57TU (335d)] rear diff is designated 215L/215LW and takes SAF-XO (75w-90) with a 1.2 liter fill.
~199K miles. I -still- don't fear my 335i.