MB fluids questions (not engine oil thread)

[ktlimq]

MB ATF, MB differential oil, MB power steering fluid seem to be petroleum based products.
However, they are more expensive than the Mobil or Amsoil synthetics.
Why?

Are they better than synthetic?

What if I have put Mobil synthetic, but an MB dealer tops up with MB fluid?
Those synthetic fluids are compatible with conventional fluids, but mixing reduces performance benefit.

Synthetic engine oils leak more. Synthetic AFT leaks more too? A book tells me to live with small ATF leakage because the repair costs much. Currently, my tranny has no leak after 1k bucks repair at dealer.

By the way, how much more expensive are MB fluids at dealer than Febi fluids at online aftermarket retailer?