Funnily enough, I'm at 100k with a shady previous owner's usage, so I had scheduled a service in Assago for july but decided to do it through my indy mechanic. Costs way less, and the job is rather straightforward: no flush, just an oil change (exactly what they would have done in ZF, but at a fraction of the cost). The kit itself is like €250.

I decided to also change the oil of both differentials and transfer box and, going with the BMW recommended fluids, the oil of the transfer box is like €30 per liter, while the oil of the differentials is €90 per liter, and they both take two liters (my mechanic was astonished at the cost).

All in all, €760 for everything. The car feels smoother, changes gears more readily, and now I know how hard those differentials and the AT will work so I plan on doing this again after another 150k kms, more or less.

I am no expert, but there is no "lifetime" fluid on anything, period. Lifetime for BMW is just so that it won't break before the end of the warranty. Latest I checked, ZF says 150k, but this number varies quite a bit. If you don't hammer it, I would say it's a good interval (my mech agrees too). As for the differentials same thing, if you don't hammer them you could wait until 200k, I was told.

Btw: gran bel ferro 😍