"it will still light but the engine quits after removing the igniter" What a pain.[:@] With my old X-C, an mc-59 would last me a very long time. It sounds like it's not the plug's fault though at this point. You almost must be running too lean(which easily ruins plugs by melting the coil) or something like that. All I can recommend is get it running rich again, even if it takes one or two more plugs.[&:] Don't give up.

The October issue of RC Driver magazine(newest release) has a section in it about reading glow plugs, maybe you could run in to your local book store and check it out, that would probably help a lot.

Good luck.