Lost my flapper (in scag) last year. Have seen posts saying replace and don't bother?
Can't imagine it was there for decor. And they don't seem to be Avilable.
Your right it's there for a reason.
Replace it.
The one in the pic looks like the rivets are about to break or come loose.
A piece of hard rubber(side wall from a small radial tire)cut to size.