seam on the sides where the panels meet and yes they leak sitting inside on the floor you can see light from outside
That's why I requested pictures, I don't see how you could see light on a overlapping seam that isn't damaged in some way.
On a seam that overlaps, if it leaks, I don't really see any way of fixing it other than take it apart and apply sealer where it overlaps. I don't see that slapping something on the outside of it would do much good, maybe short term. If you put it on the outside it will maybe work for a while, but look bad. If you put it on the inside, it may keep the water out, but water will get in that far and probably rust.