If it was only a little fluid then it was indeed most likely from the 93 replacement. Booster works on vacuum, using the outside air pressure to push and assist. If the amount of space on the vacuum side is decreased by fluid then the amount of pressure generated is decreased. Like wise a rip in the diaphragm (almost certainly what you had) would decrease the assist. Both leading to hard brakes.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42