yep - sounds like a boiling problem. I bet if you flush the fluid you may even find it a bit emulsified too and loaded with specks of rust etc.

New fluid always gives great pedal feel no matter what car.

If you lack a pressure bleeder and even a helper - this works like a charm.

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_9020969-P_x_x?cm_mmc=ACQ-_-Google-_-enhancedRM-_-9020969&ci_src=17588969&ci_sku=9020969&ci_gpa=pla&ci_kw=&gclid=CPGdlsbwpLcCFU1p7AodgwIA_A#utm_source=acq&utm_medium=google&utm_campaign=enhancedrm&utm_content=9020969

takes an hour tops with 1 quart fluid bottle.

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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)