Thanks for the picture and more info. I haven’t heard of anyone trying the Seam Grip trick, but I was going to suggest something similar. At this point, I don’t think you have much to lose, unfortunately. If the Seam Grip doesn’t work, you could also try scraping a bunch of TPU off of some scrap fabric and melting it into the divot (after cleaning everything thoroughly), and then cut the TPU with a razor blade in line with the old surface to create a new sealing surface. I have no idea if it would actually work though. I’m pretty sure TIZIP would say to just go ahead and replace the zipper.