30w was the oil used for lubricated torque in the studies I've found. Also it's the only way to get repeatable clamping values: dry torque will take about 10% more torque each time to achieve the same clamp force. It's surely why TTY is used whenever a tight tolerance is needed for clamp force.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)