why would you want a one-way in a mini...
You would have absolutely no braking affect going into the turns... it would just roll forever. On a tourer it's different, as you have the rear diff helping to slow the car, but in a mini, they are freewheeling anyway. So if you put a one-way in and you'll have four wheels freewheeling as soon as you come off throttle...
But if you want to run one, well, I guess a TA03 one would fit, as it's the same size etc as the ball diff
