Unfortunately there is no other fluid you can use AFAIK if the SLS is in the car, something about its properties and the fact it can take the pressure of the car's struts, etc.
However, on SLS removed cars, and do not quote me, you can use regular PS fluid.
Mine has been removed for a few years, and I quite honestly do not feel like risking any damage, but it is something to consider.
One of my capped off SLS lines started leaking prefusely over the summer, I went through ab0out 5-6 bottles of the CHF7.1 BMW fluid, and man, it hurt. LOL
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