Detroit locker posi unit??

Has anyone used these? Know much about them? I have one in my 68 cuda. It seems to have alot of slop in it. 1/2 driveshaft turn in gear. They throw out of posi when you corner. Do they typically have slop in them due to that feature? Is it a case of bad spyder gears? or do they have something different in them? I never have worked on them other than putting the ring and pinion in some time ago. What is the most dependable posi unit for street and strip with a 4 speed and slicks?
Thanks for all replys..
T.J.