Welcome to the fest!
Not preloading the bearing will result in just what you had happen. The previous one probably cracked because it was old and worn out. The crack was a result of the loose motion from wear, and that transferred to the mount.
Did you keep the front driveshaft in register with the rear when you replaced the CSB? They are balanced as a unit, and if you get it turned so that the two parts don't align the same as when they were made, you get vibration and premature CSB wear.
Quotes to live by:
guessing gets expensive
nothing is more expensive than a cheap BMW
Ken Kanne, Silverhill, AL, Honorary Forum Grandpa/Craigslist addict/Hoarder of all sorts of stuff
1995 318is "Bebe"; 1993 325is "Elvira" 1985 635CSi "Katja" 1984 633CSi "Sylvia"
I NEED A NAP, DANG IT!