I'm not sure if this is true but I have heard that there's a little filter in that reservoir. And it's a good idea from time to time to replace that reservoir. I replaced it along with that hose, as it was leaking way worse than pictured here. Not too expensive. I figured leaks also allow dirt in and any dirt in the steering rack is not good.

I replaced the E36 rack with a reman one for about $400. The original one was leaking so bad. The e53 rack when I first checked it was like $1200. No dirt in the steering rack.

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'05 E53 3.0 6mt
'17 F30 340ix 6mt
'96 E36 328is, in progress