The problem with location is that if it hits the stiffening plate, all bets are off the original source.

Since it's relatively cool out still you can run without the mechanical fan (I didn't put mine back on yet). Remove the fan and you can easily see the entire front of the motor to determine if the leak is from motor mounted part like the thermostat.

The usual culprit is the reservoir and that is usually pretty easy to determine. Again with the fan/shroud out it is much easier to determine.

The aux pump is right above where you are describing so that might be an easy thing to rule out. You may have to remove the air box to get a look but that's easier than the fan.

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