Best Way To Plug Reciever Crack?

I have a King Zephyr Baritone that has just been repadded. It was playing terribly, and I had a leak light in it etc. and it is sealing perfectly. I finally figured out that the sliver in the receiver (that allows it to be tightened around the neck) has been extended so that it goes below the neck and air leaks in. When I plugged it up with cork grease the horn started playing great.

Does anyone have any advice on how to best plug the crack in the neck receiver? I don't know the correct term for it, but there is a slot in the receiver that allows it to be tightened around the neck. Cork grease is a short term fix, but I was also thinking of chewing gum and teflon tape as another method. There is no repairman in this country, and this is a school horn, so I am hoping for a more permanent solution. Any advice is much appreciated!
Nathan