I cannot tell anything from the picture. But I do know from my experiences, dealing with old tanks can be a nightmare. I had one 30 Gallon start leaking from the bottom two months after I started using it, what a mess! I digress, I wonder if you could convert the top bracing to a euro-brace. You could get glass cut to the exact size at a local glass/mirror shop (or do it yourself), if you do this, just make sure they do not 'polish' the glass. But be careful, it is super sharp!
Otherwise, you can buy new plastic bracing online. Either way, I would replace the whole bracing to ensure the integrity of the tank.