Thank you all so much,
It makes total sense that the frame would be exposed from to the supply to the take up and that the line would appear depending on the ambient light and how long the film would he in position. I will check for leakage when this spool is finished.
I would like to send the camera in to get the seals re-done - any recommendations? I am prepared to send the body in via post as I am in D.C and there are not many good camera shops around.