This is a must-do. I changed my '88 Honda Accord's fluid yearly for 8 years, and even with 280+k miles not a single brake part has failed or been replaced. I follow this recommendation religiously, and strongly suggest you do too. Brake fluid is hydrophilic (loves water), and absorbs as much as it reasonably can. That's what darkens the fluid.

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Best regards, Michael
'92 500E
'88 300TE