use an ATF in there - saginaw type power steering fluid is quite thick when cold (good boost assist) but really taxes the pump if not made for it.

If you want an undyed ATF that you see what the factory filled then you can buy it at NAPA - its sold as Lubro Moly steering gear oil. I think I saw it for 8 dollars a litre and its basically dexron II with some stiff antifoam additives.

I have used it in toyotas as it matches the factory PSF color of theirs.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)