Don't know if your situation is similar to mine or not, but I had #1 break off in my 210 chassis last fall. If the hex head is still there, I'd first try to use one of those sockets that grip on the flats of the hex. My guess is that you are beyond that point however. If the hex head is gone as mine was, what I did was drill out the center heating element pretty far into it. I then removed all of the threaded part of the glowplug first by using a drill bit just large enough to take enough metal off of the glowplug threads to weaken it enough so that I could pry the threads off and out with a small screwdriver and pliers. At that point the glow plug was just kind of resting/stuck in the head. Then I took a drill bit that was just the same size as the inside of the metal sleeve of the glow plug and tried to drill that out. Hopefully what will happen is the drill bit will catch and pull out the remaining piece of the glow plug as it did on mine. Sounds like a lot of work, but it sure beats having to remove the head to have a machine shop drill it out.

Len