We have this problem as well. The only real question is which adhesive to use. A solvent-based liquid, such as Goop or contact cement, will probably dissolve the foam inside the cover and cause more problems than it solves. An epoxy might work as long as it was liquid; a polyurethane would work better, but needs moisture to cure. Perhaps injecting a little water after the adhesive might work, or wrapping the repaired area with a moist towel and plastic wrap to humidify it. I did succeed in finding a veterinary syringe that has enough pumping power to move the thick adhesive: buy it at a farm supply store.