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I suspect there is a vacuum seal between the MC and booster (sealed w/ flat O-ring) since my M-B cars have a similar-looking pancake booster. If true, a rear fluid leak from the MC will flow fluid into the booster (as my M-B). On older Mopars, there was a "drip gap" between MC and booster, and the booster had an inner bellows around the output shaft. That made the boosters thicker. So, when you change the MC, look for fluid inside the booster. You might stuff in rags to get it out w/ capillary action. Normal glycol brake fluid absorbs moisture to cause rust, so you probably don't want any sitting inside your booster. It should be much easier to replace just the MC. The booster requires crawling under the dash, which is always fun. Bench-bleed the MC to get all air bubbles out, and flush new fluid thru all the tubes after install. You should do that every 4 yrs or so, regardless just to fight moisture, especially for those living in the East. I use silicone fluid (DOT 5) in most of my cars so no rust. I even put it in my 1996 Voyager last pass, even though it says "not for use in ABS systems". I just had to test that lawyer-speak. The brakes work normally and I get the proper ABS "chatter" when I skid in a wet parking lot. I suspect they simply didn't qualify the system w/ DOT 5.