Broken R12 parts I've seen:
-lower pivot ball screws
-hub carriers (they don't usually break, but the pivot ball screw breaks and leaves part of it into the hubs, making them somewhat useless)
-lower pivot pins (usually bent, not broken)
-upper suspension mounts
-lower front bumper brace
-front plastic driveshafts (replace with metal). I'm still using the original plastic ones in the back after >10 hours of racing
-driveshaft blades (check those after EVERY run. During practice, after every hard crash. If they look at least a bit suspicious, CHANGE. If they break, they take diff outputs with them -$$$).
-diff outputs (see the previous item)
-rear belts (due to wear & tear really, not crashes). If stone gets caught between belt & diff pulley, it can munch the pulley too.
-siezed clutch bell bearings (again, wear item)
-exhaust pipe of the muffler (happens with all the cars)
It takes a hard crash to break this car, but I've also seen whole suspension of one side wiped off. Never happened to myself though