I had a pair of waders that got that way after nine or ten years of hard use. I figured I had gotten my monies worth out of them & had nothing to lose by trying to fix them using Pliobond. In the end I ended up sending them to the manufacturer, who told me what I expected. I had worn them out & they were ready for the wader graveyard.
Glad the Flex Seal worked for you. Keep us updated. Pliobond is becoming difficult to come by. Meanwhile back at the ranch,,,I discovered several sources for inexpensive waders & purchased a pair to hold me over until replacements for my favorites became available. Having found them, I now have a backup pair of waders.
Perhaps this comment is out of place - and I have no commercial interest in them - but seam failure drove me nuts until I purchased LL Bean's superseam technology Kennebec waders. Basically, these waders are unsewn. They simply overlap the parts about an inch and glue them. There may be better waders around, but I have found Kennebecs to be the best I have owned. Other manufacturers should try their approach.