As above!! What type of shafts are they being copied from?
I've never broken one, the only person i've ever heard of breaking one was in a dr30 with near on 300rwkw, and he shattered a cv joint due to old age more then anything!!!
If you want a good OE replacement half shaft, get the R31 import half shafts, but you need the stub axle and everything, and they are meant to bolt straight up (both DR30's and import R31's had the long nose R200 LSD)