Let me tell my point over here:
My car has 195K and the brake fluid was never changed.
I did the "turkey pump job" 4 weeks ago, the fluid was brown( even had the impresion that the fluid tank is dark) but when I did put the new fluid in it was clear yellow. After two weeks the fuid un the tank was brownish again but not that bad as the first time. I did change it again with fresh fluid and is much cleaner now.
The point is that the temperature of the fuid in the calipers is way higher than in the engine compartment. So hot fuid goes up and colder one gets back to the caliper.Conclusion is the the fluid circulates ....

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New Addition to the family
2013 Passat TDI 5Miles
2004 E500 4MATIC Wagon 95k
1996 E300 Diesel 173k Sold
1993 300E 2.8 230k Sold
1994 E320 White Wagon 373K Sold
Still dreaming about ....500E


Radu Negru