Epoxy Putty . Several companies make a two part putty , it's not runny like epoxy glue , mix the two parts together and mould into place .
I've found it in plumbing dept . and automotive dept. .
The first I ever used was for repairing leaks in car gas tank ... the stuff sealed the tank while it was still leaking and hardened like a rock .
Plumbers also use it on leaking pipes .
J-B Weld , PC Products and Gorilla all make epoxy putties ...note do not get quick hardening it's not as durable as the slow , 24 hour hardening epoxy .
Gary