If you have a problem just open them up and let them gravity drain into a cup at each wheel at the same time...takes about 20 minutes and then pour some clean fluid in behind the dirty and when you get clean you know that the system is clean...you might get clean in front before the rears..if so shut them off and keep draining the back and keep filling the reservoir...I don't think you will have to fill it 2 times...then I use valvoline synthetic brake fluid...jim

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James A. Harris