Hi:
The mechanic who lets me drive my '84 westfalia if I don't over extremely
abuse her, resolve this problem very easy, effortlessly and cheap.  He took
out the screw/plug from the radiator top and with a hacksaw cut a groove on
the bolt side up to the middle.  Now the only thing to do is: loosen the
bolt three or four turns; let air out until it bleeds coolant and tight the
bolt.  No burns trying to start the thread.  Hope this helps someone.