I used DUM DUM a lot in the 70's when I was installing aftermarket air conditioners in cars. I haven't looked for it for a long time, but it should still be around.
I wonder if plumber's putty would work. I was rewiring an old Coke machine for a friend a couple weeks ago and we went to the local hardware store to buy some plumber's putty to replace the dried up stuff covering where the wires exit the cooling box.