The driveline is pretty solid really, the driveshafts take a while to wear out unless you constantly mash the throttle & try to do lots of wheelies/ backflips.
Otherwise, diffs are the next weakest link- easily fixed with some FLM hybrids, UE Ultralites or some modified LST2 diffs.
Hotracing & RobinsonRacing make upgraded slipper clutch units too, though the stock one is fine if you keep it fairly tight, but consider some of the metal slipper pads:
http://www3.towerhobbies.com/cgi-bin...?&I=LXZUH8&P=7
though Im not sure if those come as stock or the graphite? pads do still...