No joke, my 125G did the SAME thing less than a month ago, same tank with the stupid miter cut trim around the top. Admittedly yours is in better shape than mine, I just keep it full of guppies in my garage. I resealed it, let it sit for about 4 days and filled it up. All was well, for giggles I put my two Emperor 400's on it. Immediately another seam started pulling away. I caught it and clamped it back together, putting silicone back in the crack that opened up just in case. I also used plastic bond epoxy on the top trim in the miter cut since it seemed like the trim pulled apart and took the glass with it. I wound up getting 2 1.5" 4' pieces of steel and bending them so they went around the corners of the trim, and clamped them on with JB Weld epoxy to hold them. I really, really don't want to have to clean all that up again. Good luck!