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Seems to be fine, have glued a few flexi spots on boots and seems to last fine as long as you prep them properly before gluing. Also heating up the area your gluing with a hairdryer beforehand helps...

How old are they? I'd take'em back if they aren't that old.

Otherwise I've found the best glue is to use Ados F2 glue. clean the 'wound' spotless and rough it up a bit with some sandpaper then...