Place a negative with the light leak on the film plane as it would have been during exposure, emulsion toward the lens, image top to the bottom of the film plane. The light leak on the negative will show the section of the holder where its coming from.
Thanks. The light leaks are on only two frames that aren't sequential. I checked around the area of the roll film back with a flashlight, and nothing stands out.
Is it the dark bar thing that runs all the way across the image? It continues outside the rebate (the clear edge of the exposed frame) and thus is not a leak from the "front" of the back. For example, it's not the kind of leak that is caused by the back pulling away from the rear of the camera. You may want to look at the light seals at the hinge and latch sides of the back.
Agreed, a leak at the hinge or latch
Edit:
With the holder loaded with film and closed is there any movement of the shell back?
With the holder open is there any play in the hinge?