Did it ever work properly? I would look for a round medium strength magnet and glue it to the door at the top or bottom (or maybe both). Of course, I'm assuming that it is supposed to hit a metallic rail at the top or bottom that it's supposed to stick to?

Are you having a framed shower door? That's the common problem that most people really encounter with a framed shower door. And having the right specs for repair is so hard to find. I would suggest you upgrade your shower area with a rather frameless door because it is more convenient. Trust me it works fine and easy.