Light leaks on rolled film (not 35mm) generally occur at either the first or last frames of the roll and are generally caused by operator error when loading or unloading a body or film magazine. On 35mm cassettes, it usually appears on the entire roll typically on reused reloaded cartridges or on the first and last frames if light trap is loose.

If it's a light leak on the body or film mag, light leaks are generally consistent throughout the entire roll although sometimes depending on the type of mag or body, they may appear worse towards the end of the roll as the take-up spool becomes thicker with exposed film.

The best place you can look for leaks is on the negatives or transparency stock and pay close attention to the film margins. Put them on a light box or some source of illumination. Look carefully for streaking in places that normally don't get exposed to light as the rest of the frames do since leaks tend to know no bounds so-to-speak and unlike something like lens flare which is bounded by the frame margins, they tend to overlap into areas that normally contain the frame number and should appear otherwise blank. And, like a broken shutter, they tend to show up fairly consistently from frame to frame in about the same place (although not always).

If you don't seem to have those things going on, THEN I'd look to the processing and tell us what kind of tank you're using, etc. as light leaks can occur there as well. Then again, I'd look for some kind of consistency there as well. All frames, some frames, all rolls, some rolls, just one roll?

As they say in Seattle (and Chicago sometimes)..."Where there's smoke, there's usually salmon".

Take it light ;>0
Mark