My experiences are totally opposite to yours. Upon recommendation of Turner Motorsports, who still races E46 M3's, I purchased their package of Redline automatic transmission fluid D4 for my transmission and the differential Redline fluid for my diff.I would definitely go with the oem bmw fluid with fm. I have Royal Purple transmission fluid in my e39 and it works well. But for the differential stick with the oem one. My mechanic went and made an executive decision himself to use Redline and that was a big mistake. Horrible grinding sounds when turning. Swapped it for the oem fluid and my car is much happier now.