Rick- they are supposed to the be the same, maybe the graphite was from different batches?
forty6- I've seen the diff screws break before but it was usually running carpet with foam tires. We crank down on the front diff to make it really tight and it stresses the screw pretty good.
Yokomo king- I've gone through a handful of the plastic drive cups already running mod. I put an aluminum one on the rear of my car since that's the only one that's broken so far.