I was doing my monthly read of Engine-Builder.com and I came apond this idea that just makes sense.I would think some of the"oldtimers" know about it already,but I thought I would share it will all of you anyways.It's kind of cool:

If you use heat to remove broken bolts and studs, try the following procedure:
Coat whatever is left of the broken bolt with wax and then apply enough heat for the wax to melt and run down into the female threads of what you are removing the broken bolt from. After you have drilled for an easy-out, apply the necessary heat as you normally would to remove a broken bolt.

Note: This procedure is not always successful for broken exhaust bolts, but it works very well in other applications.

Old vehicles and broken stuff?????.Well I hope this helps.The wax ring from toilets would last a long time.