Glass Cages carries a replacement for $15 if you want to go that route - it's the second from bottom on that list. I'd call them before ordering with a tape measure handy to make sure it will fit. Removing the old one should be easy with a razor blade or scraper, just make sure that all of the old silicone is cleaned off before installing the new one.
I'd give the rest of the aquarium a good inspection too, that center brace is there to keep the glass from bowing. Even if the glass isn't cracked anywhere, it may have caused stress on the seal if full of water while the brace was not in tact. In other words,
after you replace the rim/brace and let it cure, fill it up and check for leaks!
Good Luck!