Bought a bunch of 35mm bulk film cartridges so I can roll my own. They are the Kalt brand, black and yellow metal carts with the snap-on end caps. (Made in Spain.) They work well but, after about 3 or 4 uses, I start seeing dark streaks (light leaks) along the edges, outside the sprocket holes of my developed negatives. After that, they get progressively worse and begin spoiling the film. Once the light flashing gets past the sprocket holes, I have to quarantine the cartridge and use a new one. I have saved a bunch of the plastic containers from my store bought film to keep the carts in. The carts are either in the camera, inside the plastic container or being refilled/emptied at any given time. I never let them sit out or roll around in a drawer or bang around loose in my pocket. (I learned my lesson when a couple of them got banged up and I lost a roll of exposed film.) Do these cartridges have a finite life or am I not doing something right?