If you are not replacing the uni-directional clutch as a complete unit, you should at least be replacing the cylindrical roller set when you perform an overdrive rebuild.  These rollers see tremendous compressive loading, and they are prone to fatigue induced failure after many years in service.  Always fit a new uni-directional clutch a whole, or at minimum this replacement roller set, when doing an overdrive rebuild.
Sold as a complete set of 12.  Fits all A, D, J and LH overdrive units found in British sport scars.