Weird doughnut shaped flapper

Got a weird designed flapper that looks like a doughnut around the overflow tube. It slides up and down on the tube to flush. It's leaking, and I've never seen one like it, looked in a few stores nothing will work, any suggestions?

Posting a picture would be a big help.
Mansfield and old American Standard had a dropping tower with seal on the bottom, not sure if thats what you mean.

flapper

Unless it is really old, it would almost have to be a Mansfield and Home Depot has the replacement, but there are two different versions but you should be able to tell which it is by viewing the replacements.