You'll want to check the bottom edge of the film door towards the take-up side. Could have a little bend in it, or the seal is not correct in that area.
But it depends on whether the leak is from the front or back of the film. Check the negatives to see if the leak strikes the sprocket holes. If it does, then it's from the film door. If it doesn't, then it's coming from the front somewhere. There is a foam gasket that fits over the rewind shaft that can cause problems.
Another clue is the color of the leak (and this is particular to color film). With a red cast, it would be coming from the back of the film, shining through the anti-halation layer with just enough strength to affect the red emulsion layer. Since it is blueish, it should then be coming from the front.
Waiting for the light