left bleach on tub drain...
I just bought a replacement for mine yesterday. The one I'm replacing is only a year and a half old. It's the kind you push down to close the drain and push down again to open the drain. I won't buy that kind again. I've talked to a couple other people who have had problems with theirs too.
When the last one was put in, I had to go buy a special tool to install it. It might be called a drain wrench (not sure of the name). When you're at the store, ask someone in the plumbing dept. if you need to get one to install your new drain. Or, better yet, maybe someone here will be able to tell you.