Gearbox tail- shaft oil leak 1960 smooth case box

[Ragtop733]

I have an oil lead coming from the gearbox tailshaft. I have replaced the seal twice but leak persist on further examination it would appear that the seal is not the problem, it looks like the oil is passing through the spines and coming out at the prop shaft front yoke dust shield. To be clear the seal is working fine and is not passing oil but the oil is escaping through the splines at the sliding coupling, has anybody else had this problem and is there a solution? I have been told that some early models had a cork packing joint in the prop dust shield and that others have packed the shield cap with grease which helps to keep the oil in place any advice would be appreciated