Mine has the same problem.
I checked out what was avalible in Time Serts so I could put the stock =
plug back in. No luck.
Not only did the PO of my van put a spark plug in it, he put a theaded =
insert in first. So to
put in an insert that would make the hole the right size for a factory =
plug, I would need an
insert that is about 5mm thick.
What I did was take all of the ceramic out of the plug, and filled it in =
with weld. Then I drilled the
plug so I can saftey wire it in place (an aircraft thing).
I would like to fix it right, but that combined with all the other =
problems makes a new engine
or the 30,000 mile 84 camper I found more cost efective.

David