Hi Dan, it’s hard to know for sure without seeing it, but if there’s already glue in there then you probably won’t be able to heat seal the pieces together and you’ll have to use more glue. A thick layer of Seam Grip or Aquaseal might do the job – sometimes I put a piece of fabric over top of the glue for good measure. Other people have recommended a glue called HH-66, but it’s not available where I live so I can’t vouch for it personally. If you’re considering an internal patch, I would look for HH-66 and give it a try on some scraps first, because Aquaseal and Seam Grip are great for filling small leaks, but not so great at gluing pieces of fabric together. Cheers!