D4 was a preferred choice for many XI owners with the GM trans. I've read several posts where it has been stated - D4 is VERY close to the original factory (Texaco) spec. It has been in more recent years that BMW recommended Dex VI as a replacement. D4 is known to blend well with the remaining fluid and be chemically compatible. User tested - user approved.
You're fine and D4 is going in my ride (74 K mi.) next spring.
Anything made can be made Better