brake fluid flush every 2 yrs is a very good idea - but you probably wont notice a measurable difference in braking performance or feel b4 & after fluid flush.

btw, this is a fantastic DIY procedue to learn, yes brakes are a critical safety issue, but if you go to a dealer for a brake flush, chances are it'll be a novice HS grad kid who'll do the brake flush, master techs wont touch simple things like this.

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Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe