I have bought a 91 325ix in very good condition. It needed only one major thing, the dreaded transfer case. After searching around for an expensive used one with no garantee of how long it would last, I bought a new one from BMW. A very expensive part, about 2K. It is reccomended that the first fluid change in a new/rebuilt case be at 2000KM or 1200 miles. I am going to use Redline synthetic fluids but have one question. They have a product called D4 ATF which they state is better than their standard ATF. It has better gear lube abilities and shear properties. Since the transfer case is a bunch of gears, chain and sprocket and the sealed viscous coupling, it seem to me that the D4 ATF would be the best for the transfer case. There are no synchros or other normal transmission stuff in there.
I want to use the best possible lube and change it much more often than needed to make sure that the transfer case lasts as long as possible as it is an expensive part of owning an 325IX. The normal lube that BMW reccomends is standard Dexron II ATF. Does anyone have experience with the lubes I am looking at? Any help would be greatly appreciated.

Thanks Again
Tim 91 325IX