Hi, my 86 Vanagon is overheating.  I went out this morning to look it
over and discovered an expansion plug missing from my left side head.
Its the plug adjacent to the coolant drain on the bottom of the head,
between the pushrod tubes.  After I vented the coolant and then opened
the radiator bleed, coolant gushed out of that opening in the head
missing the expansion plug.  HELP!  I don't know what to do next.  Can I
just tap in a new expansion plug into the head and test to see what
happens?  Could the pressure been so great as to blow out the expansion
plug?  Could the head be cracked?  Any help would be gratefully
appreciated.

Thanks in advance, zyno.