Sorry but I will have to disagree with you on that. When road racing, you are trying to be as smooth as possible. You are trying to use every single inch of the track to maintain momentum. The absolute last thing you want in a turn I s the car to become unsettled as the rear abruptly locks up as with a Detroit locker. That can push you off your line and cause over/under steer in a heartbeat. In racing you really don't want to make contact, ESPECIALLY in vintage racing where yea, everybody wants to win, but the cars are really the star of the show and the point of vintage club racing is really to run the old girls. Not a big deal on dirt track where breaking traction is intentional. With an open diff, if you break traction in a turn, once again the car becomes unsettled as it has the same effect as lifting off the throttle. Your car also slows as applied power is lost, so you now have a car moving off it's line, and decelerating at an unexpected time. Not good when you have other cars tucked in behind you wanting to eat your lunch like the Porches in the picture.
My best guess is they are breaking from the shock load of locking/unlocking when you go 1 or 2 off on a curb. As suggested, I would contact DrDiff..
Also don't come on here showing a pic of a sharp little Dart like that, talking about road racing, pushing hard enough to break rear ends, and not atleast post a YouTube video of some racing :)
