[racingdwarf]

thats strange, had my B4 for 4/5 years now never had a screw snap, I have replaced it about 3 times as on going maintanance, never had a prob with the screw, I have had the locknut fail once, diff just suddenly went mid race (thus why I replace nut and bolt now and again after that). I have found the B4 diff Bomb proof (unless you put it inthe wrong way round

Same with the slipper, only prob I have ever had is the locknut failing so I replace that every now & again to.

Are you using genuine associated screws that come in a little rebuild kit ??

So no help realy, I would check what richard has said for sure,