I'll just add this here from Redline's manual trans lubes PDF found here
http://www.redlineoil.com/content/fi...%2010-13-1.pdf
Quote:
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D4 ATF and High-Temp ATF provides the gear protection of a GL-4 gear oil in an automatic transmission fluid, which is far superior to a conventional ATF. This gear protection makes it perfect for lubricating automatic transaxles and high-performance automatic transmissions. The D4 ATF provides the best low-temperature shiftability. MTL® provides better wear protection in most manual transmissions which call for an ATF which can be very important in racing applications. MTL ® provides the low-temperature properties equivalent to a petroleum ATF. All Red Line transmission lubricants provide excellent synchronizer compatibility.
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Seems they're saying MTL provides better wear protection than their ATF oils. Given the power/torque of the 1M vs a 135i/335i it could be a better choice. A super thin ATF just doesn't sit well with me in a manual trans. There's more to oil choice than "smooth cold shifting" which seems to be almost exclusively what BMW owners focus on rather than taking into account mechanical/physical properties of an oil/gearbox that may explain this.