/cgl/ - Cosplay & EGL

When I was in Japan last month I picked up the bat umbrella from AatP. Unfortunately it looks like at some point in traveling back, even though I never even used it, the top of the metal tip came off. Pic related, you can see the small seam. So there's a hole up top there.

I worry if I use it with rain it would get rusty inside. I feel dumb though, is there some kind of rubber top I could put on top to seal it like a pencil topper type thing? Or any other suggestion on how to cover it? I'm not really sure what to search since it's such a specific question.