By inserting the small folded piece of cardboard under the film spool, you increase tension on the film causing it to wind tightly, thus eliminating any
leaks you might have experienced previously without it.
If that doesn't solve your leak, Please
Cable Release Storage?
When not in use, I store my cable release under the Velcro I have used to keep my back from falling off.
I'll always have my cable with me and it will be out of the way.