I've replaced the oil seal o-ring on the distributor shaft and it still leaks. Both breather tubes that vent to the cold air box are unobstructed so I don't think I have crankcase pressure issues (although the larger of the two is attached to some sort of solenoid in the cold air box and I;m not sure how this works). The spec o-ring seems loose. Maybe a slightly thicker seal would work but I haven't found one using the trial and error method.