Spring Heater Box Cleaning - Damage Found

Find conduit or something similar that will fit inside it that can be glued in.
I cant remember what we used to patch a hole in the 67. It was a 2 part roll of "play dough" from parts store. Hardened up good and was able to sand.
"Tech steel" maybe?
Do yourself a favor and relieve the pressure off of the spring clips before reassembling. No reason for the.clips to be as tight as factory made them.