Manufacturers "specify" not-so-common formulas in the hopes...
I think that you are right on! I've been looking for "Euro" only fluids for my 540i with little luck. I'm pretty sure that I'll go with an Amsoil or Redline LSD 75W-90 Hypoid Oil for the rear axle, but I'm scared to run anything but the specified Esso ATF in the ZF 5-Speed auto transmission due to its complexity and $. I've got the filter kit ready to perform a trans service, but am kind of stuck with the fluid.
I have been trying to hunt down the following 2 fluids, please let me know if you have any sources.
Automatic transmission fluid for a ZF 5HP24 (A5S 440Z).
Recommended fluid: Esso ATF LT 71141 (BMW P/N: 83.22-9 407 807)
Final Drive Oil: Castrol SAF-XJ or SAF-XLS (BMW P/N: 83.22-0 002 094)
I have found the Esso ATF for $15-$30/liter, and have found no sources for the rear axle fluid.
I too feel like BMW has specified fluids not available in the USA to try to make me a prisoner of their dealerships. In case you are wondering BMW techs are instructed to recover and reuse this "Lifetime" ATF fluid any time they service/repair a trans. I beleive it was someone on this board that stated that the only lifetime fluid is in your spine. I like that statement and have been using it, I hope I haven't violated your copywrite.
1998 BMW 540i Sport
1989 BMW M3
1979 Triumph TR7 (1st car)
1986 BMW 735i (Sold)
1980 BMW 320i (Sold)