Both my 300D's had brake fluid inside the booster. It was a bit hard to get it out since it doesn't all run out under gravity. I had to stuff in rags to absorb it. Each car was not being used for months during this, so I had leisure to do it right. Both cars got silicone fluid (DOT 5) w/ their new MC's, so little concern w/ rust, which is the main thing that causes the seals to fail.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans