The oil port is for keeping the braking clutch oiled. The drive "pinches" a cone shaped area on the chain side of the hub, some times they can be just jammed up with old grease and dirt or metal filings. Unfortunately they some times wear down or grind off due to abuse or lack of maintainance. The best thing is to open it up and clean it really well, especially inside the drive "screw" and the drive "cone", and if it doesn't look chewed up on the drive parts, put fresh grease all over them and put it back together. If it works, then add oil to the brakes through the oil port and ride. Hope this helps.