If you can't find a new casing, you could use some
5200 marine sealer.
This stuff is made for below waterline repairs, so it's
waterproof.
It's also an adhesive.
It comes in white and black, I'd use black.
All you need is a little squeeze tube of it, not a whole calk tube.
I'd use it very sparingly.
It takes a week to fully cure.
Good Luck.