[dwydendorf]

The original posi units were made by Eaton. I think you can still get the original type clutches through a dealer that handles the Eaton parts.
The factory clutches were broken in on a break in machine after being soaked in a pan of gear lube. You could do something similar by assembling the differential with preload plates and springs and turning the axle a half dozen times in each direction. It won't apply as much pressure to the clutches as the breakin machine did but it would be better than what you have now.