spruceflame

The metal zipper teeth are large and do not look like steel; they're dull, not shiny, and more silvery than steel is.

The material around them is a twill cloth, not plastic or nylon, so the remedy for the zipper can't be able to soak through and get on clothes packed inside.

The suitcases are of heavy, flexible vinyl or something like it.

I'd like a solution that doesn't create a build-up of gunk that eventually makes the problem worse.

The luggage is a gift gotten at a yard sale. I really need luggage, but I haven't even been able to get it open (I don't even know how many smaller suitcases are stored inside the large one; I think there are two).

Thank you all.