What part of the line is rough? The ball surface that seats into the injector or the threads of the nut. If it is the ball, that has to be perfectly smooth and NO scratches. If the nut is hard to turn, the threads may be galled. With that, you are possibly not getting enough compression force from the nut to seat the ball into injector. I believe the torque on the nut is about 20 ft. lbs. Might double check that to be sure.