Although a repair may not be permanent, you can repair either a silicone or urethane rubber mold so that you can at least get a few more castings. You can then use that a casting to make a new mold.
Use Sil-Poxy® silicone rubber adhesive. Important: all surfaces to be bonded must be clean. Use acetone or other solvent to clean the area to be bonded before applying adhesive.
Repairing a Urethane Mold
Use URE-BOND® II urethane rubber adhesive. Important: all surfaces to be bonded must be clean. Use acetone or other solvent to clean the area to be bonded before applying adhesive.