Make sure it meets the API rating in your manual. Alot of "special" blend synthetics don't meet API standards, such as Royal Purple, even though they are good oils. The long term affects on your engine and transmission are unknown.
For example Redline tranny fluid in Getrag transmissions as those found in Supra's and E39's are no good. Supra's have had their tranny's blow because of Redline oil. Always make sur you use the recommended API oil for your car.
'98 (04/98) 540i/6 Biarritz Blue / Sand Beige
Options: 17" Style 32 Staggered / Sport Seats / Xenons / Sport Suspension / 6 Speed / Cold weather Pkg
Mods: M5 Grill, CDV, AE Xenons, Rogue Engineering Octane Short Shifter w/ WSR, Rogue Engineering Performance Transmission Mounts, Royal Purple Synchromax Transmission Fluid, Gruppe M Filter Ram Charger
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