If the filters are dropped on a hard surface like concrete, they can crack. I've seen a Walmart employee dump a whole box of them out on the floor, bouncing and such, then put them on the shelf for sale. i'm sure everyone of those leaked.
When one leaks, I just throw it away and get another. At $15 each, it isn't worth a lot of work to try to find a leak.
I've also noticed the cheaper white Camco hoses often leak from the fittings - even brand new. The metal is cheaper grade and thinner than it was four or five years ago. Tighten it too much by hand or with a wrench and it stretches and leaks. Double washers won't stop it, in fact make it worse.