Here is my breakage list (what I can remember):

Pinion gears -> Replaced with stronger units that a guy in Italy had made and was selling
2 Front axles -> Replaced free with stronger units by CEN
1 Upper suspension arm -> Bought whole set off eBay
2 Servos (electrical & mechanical failure) -> Replaced all 3 with HiTec digital servos (best upgrade I have done)
Front slider driveshaft (connecting pin was twisted and couldn't be disassembled without breaking it) -> Replaced shaft and drive cups with metal Nemesis units
One-way bearing on internal shift unit -> Bought bearing on eBay and pressed into spur gear
O-ring on fuel cap stopped sealing -> Periodically replace with cheap black rubber o-rings

Upgrades that have prevented breakage:
VG rollcage
Throttle return spring